When errors are found and retained in the new Validation Issues category and they are fixed, then validation reran, my active category is switched to (so far only) Mathematical Operators.
I believe the active category should switch to the main “Glyphs” category.
I reckon this one is a bug, but I will leave it here until Erwin comments.
I had similar results in a quick test. The last Unicode character set was selected after deleing all glyphs reported with various errors.
We’ll make the following improvement with the next upcoming update:
When a category is no longer shown, the newly selected category will be the one right above or below. If the whole main category is no longer shown, the Glyphs category will be selected.