I concur that this usually happens when a patch change is embedded in the midi data for the track.
In the Track Inspector Pane, there is also a parameter there where you can set the midi track to start with whatever patch you want, using the Patch Browser button OR using the drop down arrow for the Patch parameter, OR you can directly enter a number into the Patch parameter, by double-clicking on the word Patch.
So, a small number of ways to set this that can be easily checked.
Hope that helps,
Bob Bone