I haven't messed with it in a while, but I think the real issue when I encountered this was that there was a volume discrepency between the delay blocks position in the two given patches.
That does not mean that one patch was louder than the other, it simply means that the signal was hotter going into the delay in one patch than it was in the other. For instance, if in one patch I brought the volume down by lowering the level in the amp block when I created it, but in the other preset I had lowered the volume at the master output level for the patch, I could have this problem when switching between the two patches (this assumes the delay block is after the amp block).
If you don't level your patch volumes the same way every time, this will happen. I'm bad about roughing it in with the amp block's level control and then fine tuning with the patch master (but sometimes the fine tuning isn't very fine at all really). Hence, I sometimes have this problem with my patch spillover.
D