4051 mux problem?

[Stewart Pye]

Hi...

I've built a midi to drum trigger unit. The output of the micro goes to a
DAC and then to a 4051 mux. The mux then goes to an opamp buffer with
parrallel cap.(S&H similar to paia midiCV) The problem is:

If I send 00h to the dac then switch through each channel of the DAC to
clear the triggers so no outputs trigger, they stay low for a while and
then start rising which causes oscillation of the drum oscillators. I would
have thaught that they would stay low. 

The 4051 supply is +12V and gnd. Could this be the problem? Maybe I should
use -12V instead of ground. It's not really a problem because I just keep
refreshing the mux. I'd really like to know why this is happening though.
Any ideas?? 

Regards
Stewart.