Version - Adobe Indesign CC
2015.3 Release
11.3.0.34 Build
operating on Mac OS X El Capitan, Version 10.11

Steps to reproduce issues:

Create a new document with a double-page spread in Indesign.
Import four images into document and arrange on spread.

Import a shape into Indesign that will be assigned as a pop up box that will appear above Image 1 when rolled over, and place shape next to Image 1.
Place some text (e.g. "Image credit') on top of shape and group text with shape.
Open Buttons and Forms dialogue box:
- Convert group to a button.
- Set 'Name' as: Pop up 1.
- Check box to turn 'Hidden until triggered' on.

Select Image 1 which will be the trigger image for Pop up 1.
Open Buttons and Forms dialogue box:
- Convert Image 1 to a button.
- Set 'Name' as: Image 1
- Select 'Event: On Roll Over'.
- Add a new action: 'Show/Hide Buttons and Forms'.
- Set 'Visibility': select Pop-up 1 from list and set visibility as 'show'. Set visibility for 'Image 1' itself to 'ignore'.
- Appearance: [Normal] is selected.

• Select "Event: On Roll Off'.
• Add a new action: 'Show/Hide Buttons and Forms'.
• Set 'Visibility': select Pop-up 1 from list and set visibility as 'hide'. Set visibility for 'Image 1' itself to 'ignore'.
• Appearance: [Normal] is selected.

Repeat above steps for Images 2, 3 and 4.
Export as interactive PDF.

Actual result: 3 out of four of the images will trigger a pop up box when rolled over in the Interactive PDF as exported from Indesign. The fourth image does not trigger its assigned pop up box. The settings are exactly the same for all four images and pop up boxes. The shapes for the pop-up boxes are each imported separately, not copied and pasted. Sometimes none display, sometimes all, sometimes half. I cannot depend on this feature to work correctly.

Expected Result: Each of the four images will trigger a hidden separate pop up box for its corresponding image when rolled over and the pop-up box will revert to being hidden when the image is rolled off.