HeliSetup: cannot manually set swash Bottom

Try doing this:
1. go to Heli Setup page in mission planner
2. push "Manual" button in the middle to begin setting up the swash
3. try to manually overwrite the "Bottom" value. They are immediately overwritten with whatever value was there previously.

Start by reproducing the issue on the Heli Setup page using the listed Manual workflow, then inspect the code handling the swash setup and the Bottom value. Done means manually entering a Bottom value no longer immediately restores the previous value.

Written by the indexing model from the issue text.