Hey guys,
To be honest, this is great! Just so you guys know, since 8.4.0 we added some new diagnostics mechanics in EAGLE to improve the stability over time. I added this new check in the latest 8.4.2 to find undo issues. Thew good news for you is that after the assert I also added some code to clean up the situation so you're totally fine here, there is nothing wrong with your design!
Even with the explanation every one of you provided, I can not reproduce this though. It would be great if you could send me your design with the exact steps how I can reproduce it. A video would be super helpful as well. I will PM this same message to every one of you which also includes my e-mail adress.
Thanks!
PJ
Pieter-Jan Van de Maele
Senior Engineering Manager, Fusion Electronics