Comment 3 for bug 1173611

It appears here that GtkLabel is not getting the correct calculated height when text wrapping is enabled. Probably this is a gtk bug, however I cannot reproduce it with gtk git master (I also can't find any commits that look like they would resolve the issue).

Linked branch works around the issue by disabling text-wrapping in the category pane, however its probably best to find and fix the underlying bug.