Yes, it may indeed have to do with using 3/4 time, especially if you are using 4/4 RealTracks files but truncating the last beat off of the bars.

However, there have been plenty of reported problems with RealBand ending in the wrong place, or not generating parts out to the indicated ending of the song, etc. I even have had it generate parts out PAST the ending point a few times. It is very likely a bug at this stage of the game, what with all the reports to be found right on this forum.

--Mac