Fonts sometimes change without warning
I'm experiencing some mildly annoying behaviour - don't know if anybody else has seen it? Occasionally fonts reset to the default font for no apparent reason, even though they may have been a different size/weight for some time previously. It's actually quite disconcerting.
Just a side note. The best way I find to correct a sudden font change is to Tab the row foward then Shift+Tab it back, so it reacquires the Style if there is one.
I've seen this behavior, this usually happens when I backspace an entire row, when the last letter is deleted the font changes abruptely.