Strange FontLab bug: When I make a guideline global, and select the property "visual descender", the font window view suddenly changes, all characters become much bigger, filling their cells completely, like this:

It then becomes normal again after a while, but I've found no way of changing it back. Globally removing the guideline that caused it, has no effect.
Has anyone else experienced this?
I'm using FontLab 5.0.4 on Win7. The bug is gone in the 5.2 prerelease, but that is not usable yet, sadly.