There is the circuit in the attachment, made by one of my students, which causes simulation bug under Windows 7 (checked on two different machines). I've tested the circuit under GNU/Linux and Windows XP and everything is fine. The bug is: one of instances (subcircuit) of certain circuit for some reason receives undefined inputs inside it, although it receives normal signals from supercircuit. I've attached three screenshots of three states of simulation hierarchy, where this bug appears. I think this bug is quite urgent, since there is no way to avoid it (so one's unable to continue work on this circuit). I guess unique property of this circuit is: it has quite big number of subcircuits instances.
JRE version: jre-6u24-windows-i586-s