If I want to filter on issues that do not have a particular label in them, for example "XYZ", I expected to do this:

Labels not in (XYZ)

However this filter doesn't work correctly. It only returns issues that have labels, but those labels do not include XYZ. So issues with no labels are excluded from this filter.

To get what I want I have to do this to get the correct result:

Labels not in (XYZ) OR Labels is Empty

I did some searching and found that others have had the same issue, but I am not sure if this behavior is intended or if it is a bug that never got resolved. Please let me know which is the case!