Adobe InDesign (ME) 2021, 2020, CC 2019, ..., CS6
macOS and Windows

InDesign's WorldReady settings (Paragraph Direction, Kashidas, etc.) are being stripped from a document's [No Paragraph Style] style when opened on a machine with a missing 3rd-party plug-in (like Em Software's InCatalog). This appears to happen with any 3rd-party plug-in that adds a text attribute with a prefix that's lower than the WorldReady plug-in's prefix. While the following steps use the Middle Eastern app (English Arabic), where there's a UI to see the style's empty/blank WorldReady entries, we've confirmed that this problem affects all app variants (including English (Roman)).

To reproduce:
1. Install ME version of InDesign 2021 (English Arabic).
2. Install Em Software's InCatalog plug-in (http://emsoftware.com/products/emcatalog/ ) or any plug-in that adds a text attribute with a prefix ID below that of WorldReady's 0x50f00. (The SDK's BasicTextAdornment sample will work if its kBscTAPrefixNumber is changed to something like 0x43a00.)
3. Restart InDesign while holding down Shift-Control-Option/Alt (to ensure the session workspace's [Basic Paragraph] style is rebuilt to include the new plug-in's text attribute).
4. Create a new document and add a text frame containing a few paragraphs using the [Basic Paragraph] style. This text should compose as right-to-left (the ME version's default direction, as specified by WorldReady's kParagraphDirAttrBoss). Create a numbered list, since that's a great way to see the problem.
5. Save the document.
6. Quit InDesign.
7. Remove InCatalog (or whatever plug-in was installed in step 2).
8. Restart InDesign.
9. Open the document that was saved in step 5.

Alternatively:
1. Install ME version of InDesign 2021 (English Arabic).
2. Restart InDesign while holding down Shift-Control-Option/Alt (to ensure a clean session workspace)
3. Open the attached SavedWithInCat(2021ME).indd file. (Well, UserVoice won't let me upload it. Ask & I can send directly.)

Notice that the text frame in the opened document incorrectly flows left-to-right and the numbered list's numbers wrongly show on the left rather than the right. Edit the [Basic Paragraph] style and note that the WorldReady settings in the Middle East Character Formats and Indents and Spacing panels are blank/empty. (See attached before-after screenshots.) One would expect a style to survive intact even when opened on a machine with a missing 3rd-party plug-in, but instead some of its settings may be at risk of being lost.

We've used WorldReady as the victim here, but this problem affects any plug-in, Adobe or 3rd party, that adds a text attribute with a prefix that's higher than the missing plug-in's prefix (such as Em Software's InData).

Details: We've isolated what looks like a long-standing problem (bug?) with the SDK's AttributeBossList::CopyInto(), where it stops the copy when it encounters an attribute whose plug-in is missing. Instead, the copy should continue after the missing plug-in's entry order to produce a complete list of non-missing attributes. Copies produced by AttributeBossList's Duplicate(), ApplyAttributes(), and its copy-constructor are all affected.