It's also a question that what version of the UCCNC you running?
I'm asking this, because I looked back the bug fix list today and there was a bug which did the exact same thing as you described in this thread, I think Gerry reported it a few months ago and it was fixed in version 1.2038.
So, if you using version 1.2037 or earlier than it should be the same bug which was already fixed in later versions.
The issue was that the Save settings applied slow (was slow especially on slow hard drive access speed computers and if antivirus software was looking into the file while saving) and there was no protection to not allow other button presses while the software was still saving stuff and it caused the issue, because the saving and functions calling of the settings was still going on when the g-code could be started to run in the same time.
The fix was that a label was added to the screen which shows up while the settings are saved and also a protection against button presses was added while saving was going on.
Also the save settings routine was totally changed, we made it much faster in later versions, converted the save by line to create the file in memory and then flush all in once to file, so it became fast even if the antivirus software looked into the file and even if the computer had a slow disk access.
So, please verify which version you using and possibly download the latest test release if you using an earlier one and let me know if you can still reproduce the issue with that?
Here are the test release downloads:
viewtopic.php?f=2&t=240&start=40