purity III t3-off-canvas no space on top

Hi,
i'm using the purity III template and Canvas-Menu for collapsing sites.

There seems to be a bug or an unincluded styling-code (i know it's a developer version but please check this for further versions) causing some problems with the height of the 't3-off-canvas'. It appears when the viewer is zooming in/out or just closes the firebug-window (bottom position). In these cases the height of the canvas only resizes on 'f5' - refresh.

rgds