@Claymore
looks like some sync related bug - I've got a mixed rig here: it has 370, 470 and 480s.
If I run different intensity (2 for 400 and 1 for 370) I get about 15% of shares rejected.
If all is set to "-i 2" - no problem, rejects below 1%
What rates are you getting for your 370 and what clock settings?