What Ignition version are you on? I had an issue where system.util.retarget appeared to be leaking memory on 8.1.5. Support recommended I update to 8.1.13 and the issue went away. I think 8.1.13 was the newest version at the time, so it may have been fixed somewhere between those two versions.
Some anecdata I collected at that time using two minimal projects that only had one window. Each window contained only one button retargeting to each other project:
It was support ticket #36649 if that's relevant to anyone at IA.