I've been playing Ultima 7 via dosbox, in a window, so that I can multitask, and sometimes when I go back to the window, the dialogue will freeze just before a choice. Sometimes books will also freeze. The method I use to get it unfrozen is usually to either click many times or press the space bar or some combination of that and sometimes it will unfreeze quickly and sometimes it will take some time. It seems to be very inconsistent and is generally frustrating.

I've tried various things to solve this. I've tried running in galaxy with or without the overlay. I've tried various graphic modes. I've tried running outside of galaxy with or without admin and/or compatibility mode for windows 7.

Since it happens usually during a dialogue selection, I've tried opening a dialogue selection before alt-tabbing out and that works a lot of the time, but not every time. Sometimes a different dialogue will freeze up later.

Solution:
I just tried this with "autolock=false" in the dosboxULTIMA7.conf file and that seems to have permanently solved it. I don't have to lock or unlock the mouse either, but if you need to you can use "ctrl-f10"

Alternatively you can leave autolock on and press ctrl-f10 instead of using alt-tab.