To reiterate the issues when using ZNC with more than one attached client:
Am I understanding correctly that you are connected to one (and the same)
ZNC user with >= 2 (m)IRC (different) clients? Would implementing CyberShadow's clientbuffer
solve the problems you are having?
Using this module enables ZNC to keep track of separate buffers (one for each client connecting to it). You would have to setup the client id's, for example mirc-home
then you can connect with: zncuser@mirc-home/network:password and zncuser@mirc-work/network:password. I'm assuming you have the route_replies module installed as well? (This page has more information: https://wiki.znc.in/Multiple_clients