Can't trust your tools

Sometimes, I really really hate VB.NET. I received a bug report yesterday that some things were becoming enabled when they shouldn't be. This morning, I started to investigate. Unfortunately, I can't, because if I put a breakpoint in the function which is supposed to disable the stuff it suddenly starts working properly and disabling them! Then I take it out and it stops working again. How am I supposed to figure out what's going on?