Bug: Anki Deletes most/all of my IO clozes when modifying occlusion positions

From the video, it looks like the grouping operation may be responsible.

Originally reported on https://forums.ankiweb.net/t/bug-anki-deletes-most-all-of-my-io-clozes-when-modifying-occlusion-positions/46524

Start with the video referenced in the issue and the linked forum report, then reproduce the deletion while modifying occlusion positions and check whether grouping is involved. No file, test, or entry point is named; done means reproducing the case without losing the IO clozes and adding coverage for the corrected behavior.

Written by the indexing model from the issue text.