If I create a new top level group with non-english characters (!) and try to add a new category inside using right click menu, it has no name in the pop up menu and click on the menu has no effect:
However using “+” at the bottom works fine:
Here is the name of the category if you need to test: “Еда” (means “Food”).
Addition: the first top level category appears in the menu when adding another one.
Can it it be related to saving data?
I tested it here and it’s not related to non-English characters. It appears that there is a bug in Both view where the number of row is calculated incorrectly and so the category is suggested from another row. If you do that in either of the regular views like plan, actuals, or combine, it should be fine. I will file this bug. Quite embarrassing in fact.
I’ve already fixed the other bug your reported, related to using actual decimal separator from regional settings.
Thanks for taking care so fast! 
