Something has gone wrong and you've ended up with a bunch of NaN (not a number) or INF (infinity) values. That happens sometimes with certain brushes - I was never able to determine an exact cause. Contact me via PM and I can tell you how to get a version that shouldn't have this problem as well as having a way to fix the existing damage.
One way to correct the damaged area with earlier versions of FT is to is to select the damaged area and use the Global Set operation on each of the channels with a value of 0. It's not pretty but it usually will eliminate the problem.
There was a serious bug with editing across the +180/-180 boundary in one of the earlier FT Pro versions (possibly 18.104.22.168, the update from the PF website). All I can recommend is "don't do that". Not a good solution, I know. Again, contact me via PM to find out if a test version might help.