Wiardgroup

i was trying to do this minimal "percussion" thing last night, with 
the wiard classic VCO into a wiard filter, FW sequencer running it.  
so simple patch on the VCO itself, had the sine out patched into the 
VCA 1 input, which should theoretically shut the normalled square 
wave off and just give me the sine, VCA'ed.  

but i was getting some bleedthrough of the square wave signal 
nonetheless, and of course, the filter only amplified it.  i've never 
noticed this bleedthrough through as most of my sequences have been 
rather busy.  

is this normal for the classic VCO?  i know, i know, it's an AD 
onboard VCA, whadda i want?!  but still, is there any way to minimize 
this bleed?

thanks,
alex