jit.catch~ / sampling error?

hi,

i've been fooling around with jit.catch for a bit, trying to make something like a trigger-based scope.
the problem i'm encountering looks somewhat like a sampling error.

the first channel is a sinewave, phaselocked to the 2nd channel, which is the trigger channel.

at some frequencies it all works fine.. 75, 100, 150, 300..
at other frequencies however, the output data from jit.catch~ differences per frame..
(the errors are displayed in the patch)

hopefully i'm missing out on something,
has anybody got an idea?

daan.