I made it out, but only by advanced trickery and manipulation of windows.
I use a multi monitor setup and by disconnecting the screen that perpetuum full screened to while starting perp, then i could change the full screen setting to windowed without the client minimizing on me (windows thought i clicked outside the active full screen display and minimized all programs to facilitate.
This could have something to do with the forced display adapter i use. The smaller display Perpetuum full screened to, is on the same adapter as the display i usually put the windowed client on. I think the code just picks the first display it finds and full screens on that.
Why windows would have the idea that clicking on the full screen client is clicking outside the client is beyond me tho!
Now all i got to do is get all the client settings as they were before, annoying but I can overcome that. THis feature was rushed too fast IMHO!