Beta 12: blank dialogue box

After editing a project on my iPad and synchronising it using Dropbox, I open it in Windows. Scrivener creates a backup (as always), but I get a completely blank dialogue box as well:
screenshot.jpg
– which I presume ought to be telling me something useful about what’s going on?

The project opens fine and everything seems to be working, so I think this is merely cosmetic, but I hope it’s worth posting anyway.