Latency issue or even a Live bug?

[metal_head_82]

Hey folks,

I got a serious problem using Live with my vintage synths.
I use an audio track to trigger the arpeggiator of one of my synths. The synth goes to input 1 and is routed to a summing track which the goes to the master channel.
My beats go to another sumnming channel which is routed directly to the outputs 7&8 of my audio interface (M-Audio ProFire 2626).

Until here everything works fine. But if I route the beats to the master channel, the synth seems to have an offset of approx. 15ms. This however almost equals my global latency. Changing the driver error compensation does nothing. The only chance to get them in sync is to set a delay on the beat tracks. But that cannot be the solution. I wonder why I have different latencies on master channel and direct outputs. Is that a bug or is my interface going nuts?
Or is it one of those mysterious Live-Lion problems?

Did anyone else have such issues?

Thanks in advance...

This is the setup I noticed this problem:

MacBook Pro (Late 2009)
Mac OS X Lion
Memory 4GB
Live 8.2.6 (same issues with current beta 8.2.8b2) buffer at 128 or 256
M-Audio ProFire 2626 (using 8ins and 8 outs)
M-Audio AxiomPro 49
Korg Poly61 Synth