MIDI sync with RC-505

Hey everyone, I've been lurking these forums over the past few months while getting into MPCs (yeah... I'm hooked now) but I could do with some specific help on something.

I can't get my MPC2500 to sync properly with my Boss RC-505 Loop Station. The MIDI clock syncs fine, however when trying to assign commands on the 505 to sync with the MIDI stop/start the best I can get it to do is stop the 505 tracks with about a 2 second lag.

I first thought this must be a problem with the 505, because my Roland JD-XI's sequencer syncs perfectly to the MPC - however the 505 also syncs perfectly to the JD-XI (running JD-XI as the master) and to my friend's MPC1000 (running JJOS128XL), seemingly with the same settings (sync out on, MIDI clock, MMC off)

I'm going to run the MPC through some sort of MIDI monitoring program next week when I have the time to set that up, but in the meantime does anyone have any clues? I feel like I might have missed something obvious...

Thanks.

What OS are you using . I've got two mpc2500's and the akai 1.24 is a terrible master but a good slave and the akai 1.23 is a great master but a terrible slave.