I have now seen this on Crux, High Contrast Inverse, and High Contrast Large Print Inverse. That's all of the default Ubuntu themes now, so I think it's pretty clear: this is not theme- or engine-dependent. But some themes trigger it more often than others. I'm going to leave it open on ubuntulooks though since it definitely does affect that way more. The ubuntulooks people can mark it Invalid if they want.
Another interesting note: on Crux, which has fairly noticeable window borders, the borders are affected by this bug too. That is, when the title bar disappears, so do the borders.
I have now seen this on Crux, High Contrast Inverse, and High Contrast Large Print Inverse. That's all of the default Ubuntu themes now, so I think it's pretty clear: this is not theme- or engine-dependent. But some themes trigger it more often than others. I'm going to leave it open on ubuntulooks though since it definitely does affect that way more. The ubuntulooks people can mark it Invalid if they want.
Another interesting note: on Crux, which has fairly noticeable window borders, the borders are affected by this bug too. That is, when the title bar disappears, so do the borders.