This is actually not a bug in the Cool VL Viewer, but rather a bug in post v1.18.2 official viewers... Since the Cool VL Viewer reverts the UI to the one of pre-1.18.2 viewers, it doesn't have the bug. If you look in the official v1.23 viewer sources, in llimview.cpp, LLIMMgr::toggle() function, you will see that the code is
supposed to actually toggle the mouselook off and on when the IM/Communicate window is toggled on and off... It doesn't in the resulting binary, and there is therefore a bug in v1.23 official sources !
However, the bug became a desirable feature, since the whole idea of toggling mouselook when toggling the IM floater is indeed rather flawed... I therefore made this feature part of my RevertUIChange patch, and the next releases of Cool VL Viewer will now behave in the same way as v1.23 (but voluntarily, and not as the result of a bug).