X3P Bug? - Fit to Improvisation in the middle of a song?

So I've got a song that I recorded the first 21 measures of... mostly free improvisation with plenty of rubato, and I did a fit to improvisation on it. Works, no problem.
 
Now I've got a second part that I added there from measure 22 on... and I want to do a fit to improvisation of that.  I'm having issues with that.
 
I tried doing the fit to improvisation by recording snare drums on every quarter starting at measure 21, and then copy pasting snares on every exact quarter in the previous 21 measures, bouncing all that to a single clip to select before hitting the Fit to Improvisation process. 
 
However, this doesn't seem to work.  It actually gets rid of all the previous tempo markings from the start all the way through measure 21.
 
Also, the music from measure 22 on? It's significantly slower than it should be.
 
So right now, the only thing that I see working is setting individual measure beats where my notes are for the remainder of the song, which is pretty tedious (as well as messes up the size of my various MIDI clips.)
 
Any thoughts on a cleaner/better way to do this?