If you create a section with a different time signature, JJazzLab will create the correponding song part with an adapted rhythm. This is simply the rhythm from the previous song part adapted to a new time signature.
You’ll notice that the adapted rhythm does not need additional tracks in the mix console: it uses the Midi tracks of its source rhytm (fastbossa.s629.prs in the example above).
If you don’t want the adapted rhythm, like any rhythm it can be replaced using the rhythm selection dialog.
You can’t remove a source rhythm if its adapted rhythm is still present in the song
In the example below, any operation (change rhythm, remove song part, change time signature of the parent section) which makes the source rhythm fastbossa.s629.prs disappear from the song will generate an error.
This is because [3⁄4]fastbossa.s629.prs is still present and needs its source rhythm.
In the above case, if you want to replace fastbossa.s629.prs by another rhythm, you need first to remove the second song part which uses the adapted rhythm.