I caught it not saving settings last night on 0.8.1 as well.
The trick is you have to overwrite and retype the whole entry and it will force a save.
For example, if it had 0.2, and you wanted to change to 0.1 and just backspaced out the 2 and typed the 1 it may not save. But if you delete and retype it, then it will save. Not sure if that is a full bug or just a quirk. Maybe a small bug?
The way I noticed it was when I clicked Apply, there was no re-slicing progress bar on the lower left, so I know it did not see any change. I went back in and sure enough, the change I just made wasn't there. So overtyped it and clicked Apply. Boom, it re-sliced.