The groupby widget sometimes ignores grouping on two variables

[zikooky]

Hi,
I found a difficult to reproduce bug, where selecting two variables to group by in the groupby widget, sometimes it's only done on one variable, even though both show as being selected. If i select them both again, the widget then groups correctly.
This doesn't always happen, and I've already re-selected both variables when trying to figure it out, so unfortunately, until it happens again I don't have an example ows to upload.
Has anyone notice this before?
-Aharon