Steps to reproduce:

Start ExtApp load an image an create a segmentation. Activate paint tool and click into the transversal window.
Now rotate the 3D volume -> all planes except of the transversal one are white.

This is pretty sure related to the working slice which is stored as a helper object in the data manager and on which the paint tool operated. (since moving the mouse in another render window e.g. the coronal one make all planes except the (in this case) coronal one go white)