I am also encountering this issue and the arrow key workaround does not solve it in every case.

To be clearer... To access another paper size, need to scroll down with the arrow + Enter. Cannot choose it by simply scrolling with the mouse and release.

Cannot choose another size of paper in the PRINT window. I need to use the arrow with Enter. Cannot choose it by scrolling on it, like I used to do.

Our entire team is having this issue too. We can use the arrow keys as a get around, but this trick does not work within grep. Our IT has tried many times to fix. We started a service call with InDesign but this bug comes and goes and they were not able to help. I am having this issue again right now. I have tried restarting InDesign twice which usually fixes it but not this time. I have saved my prefs and Cache and would like to send it to you. Here is link to my Drop Box. Let me know if you need more info.
https://www.dropbox.com/sh/6o24wrw7alv0ekg/AAB8pkGV49IXhuOWcdXpP7Gka?dl=0

InDesign13.0.1/OS High Sierra 10.13.1

After restarting InDesign when I go to the print dialog and attempt to choose a printer, the last printer used is stuck in the pulldown window. I click on the pulldown and cursor over the one I want and click on that printer but the original printer remains in the choice window.

My solution is to go to the system prefs and delete the "InDesign Defaults" preference file. This frees up my choice without have to restart InDesign.

I have PDF export presets set. Ever since the 2017 update 13.0, when I select one of the presets, the menu doesn't change from the previous preset.
I have a Low Res preset and a High Res. If the last setting I used was Low Res, and I now want to export in High Res, the setting remains in Low Res. It doesn't change. I have to quit InDesign and reopen, then only does it work.

I posted this but was able to resolve. I had to delete all the presets created in 2017 and then recreated in CC2018. It is working with no problems now.

InDesign CC2018 issue with changing PDF export presets. Once a document is exported with a certain preset it does not let me select another preset. I have to quit and relaunch InDesign to select another preset.

I have had this bug haunting me for the past year. I could select drop downs if I used keyboard to arrow down (but that's slower). Only workaround for me was to uninstall and reinstall indesign. Would work for a couple of days then back to the same issue. Was reinstalling 3 times a week.

Just got a new computer, all new os (high sierra), new install of indesign (took nothing from my old computer) and the same issue happened on day 1.

Too time consuming to reinstall all the time! Has anyone got any fixes?

cc2018: when creating a new swatch color mode (CMYK/PANTONE/ ...) is not changeable. it always stays in the same mode as the last chosen swatch.

It just happened to me again. Per your request, here are the Preferences and Cache:

https://www.dropbox.com/sh/pi4p6g3955g2q24/AABEuDSmXweSHz7UgEfuD23Sa?dl=0

Ravi:
Please specify the exact locations of the files you need and I will post.

Thanks!

Having the same problem. In some instances I can type in the option I'm wanting, hit return and it will adjust the menu selection. That said, it's very annoying to not have menus function properly.

Upon first startup of my computer, and first startup of InDesign, I cannot make any selections from any and all drop down menus. I can change what is selected if the field is highlighted and using the arrows keys. However, when I click with my mouse to make a selection, it registers the click but does not change what option is highlighted. If I quit the program and reopen it, this bug goes away. I typically have this happen daily, however every now and then it does not, which makes me think it's because of some other program or function running on my computer.

When I try to change the Start Paragraph dropdown menu in Keep Options and I click on another option than the selected one, the dropdown menu closes but the value doesn't change. If I want to change the value to In Next Column (or any option) I have to click with the mouse so the dropdown menu opens and then use the keyboard arrows up or down to change to the desired option and press return.

Thanks User for reporting this issue you are facing, please confirm if you are facing this issue with any other dropdown widget as well.
Please follow steps mentioned at https://forums.adobe.com/thread/526990 for trashing preferences, then try working with the justification drop down and confirm if it starts working for you.

Thanks
Monica

My coworker has had the same problem since updating to 2018. She is on a 13-inch macbook pro (early 2015) running El Capitan. My drop down works fine. I am on a 15-inch macbook pro (mid 2014) running Sierra.

Using InDesign CC 2018

This happens regularly, though there doesn't seem to be specific steps to reproduce:

Open a ID file
Select an object - for example a rectangle
Open Swatches panel and try to scroll down list using scroll bar to pick a color
Sometime cannot click on scroll bar and mouse movement up/down moves list but cannot get to swatch desired

See attached video for demo of problem.

I am having the same problem trying to use find and replace or find font! Only works with arrow keys or manually typing name of font. Indesign cc2018 on El Capitan 10.11.6

I have this in InDesign CC 2017 (12.1.0.56) running on Mac OS 10.12.6. Suddenly, selecting options in dropdown menus doesn't work. For example, selecting PDF Export pre-sets.
Quitting and re-launching the app seems to solve it, temporarily.