Reason sounds like shite and plays like a toy. 'Nuff said.
I've been working away at new tracks in the 6 days that I've owned this thing. Got ~4 that are getting mature now, but I'll still miss the loss of the ~20 beats that will be stuck on the computer if this turns out simply to be part of how the MPC works. Re-creating them manually would just be silly and who really wants to show up to a gig with a PC..
This may sound like a no-brainer.....but are you sure you have the tempo set right?
Also, if you have pitched the samples at all, this will effect what the tempo setting should be since pitching up or down changes the lengths of the samples.
But, since you're making drumNbass type stuff, you're probably not using the original tempo of the break.