Odd change to VM behaviour in XEmacs 21.0?

I have noticed a change in the way VM 6.51 behaves on XEmacs 20.4 and 21.0, but haven't been able to understand why. It has to do with VM's toolbar, which it positions by default on the left side of the frame. VM uses set-specifier to set left-toolbar-width. In 20.4 this appears to trigger a resizing of the frame to increase the frame's width by left-toolbar-width. In 21.1, a resize seems to not get triggered. This generally leads to 72-column-wide windows in that frame, but occasionally results in the VM toolbar overlaying 80-column-wide windows, and display competition between the text in the windows and the toolbar buttons. Any ideas why this is happening? Cameron