Looks like the fixes for other LIM not clickable bugs that landed in 15.04 development release resolved this bug.
Besides VirtualBox is a Qt app and this bug is a duplicate of Bug #1312137 which was fixed recently in Unity release for Vivid.
Looks like the fixes for other LIM not clickable bugs that landed in 15.04 development release resolved this bug.
Besides VirtualBox is a Qt app and this bug is a duplicate of Bug #1312137 which was fixed recently in Unity release for Vivid.