After I resize a window with two panes (split view) open, I will often see odd refresh behavior in the top window. Strangely, resizing the window beyond a certain size eliminates this, as does working in a single pane.
Also, while dragging the widget, the window content is fine. It only appears distorted after I stop and only when the window is a certain size/shape.
I have seen this one before, so has Keith. It is an odd Cocoa bug. He has been able to reproduce it in other applications using the rich text widget, too.
Yes, as AmberV said, this is a bug, but it is an Apple bug - I have been able to reproduce this in TextEdit. Because of the more complicated resizing functions going on in Scrivener it seems to occur a little more often, but it is definitely the same bug, and one we have to hope Apple fix.