I want to report this is a bug.
I have narrowed it down for reproducability to this setup:
1. Create a combobox
2. Make a comment in the items field, like this

3. Set IsSearchable to true

4. The following error shows up:


The error disappears if you:
- set IsSearchable to false
OR
- remove the comment, toggle IsSearchable to false and then true again.
Feel free to check this out and report back.
I would love to be proved wrong.