Erik Spjut wrote:

>Most timing things in Csound run at k-rate not a-rate. Unless your timings
>are always exact multiples of a k-frame you'll find inaccuracies. Try
>running with kr=sr and see if the problem goes away.

It goes, in this example program (now tempo is 134.955), but unfortunately 
it does not fix the problem in the real program. I still cant run two 
instances of the sequencer instrument in synch... But Im using odd timings, 
which might lead to some sort of round-off problems. I'll replicate the 
situation in this example program, to see if that has something to do with 
it.
Thanks for the tip. I really was implicitly assuming an a-rate timing, and 
it was good for me that you pointed that out