Renoir-

>My next step is to start breaking apart the combobox class, but this will be an effort as it was initially built from someone else's class and modified to work in my particular situation. I was hoping by understanding what might cause an object to lose focus I could limit the scope of my troubleshooting.

I think this is probably best. It sounds like the combo is overloaded. Otherwise you're taking stabs in the dark. And what we say generally may or may not have anything to do with how your code is working. That's pretty frustrating for everybody. If a combobox is too complicated to follow it's events, then it's design had probably gotten out of control. It might be that it needs to be an abstract class with some functionality with a concrete class with other functionality.

No need to split it out, though. You could either 1) start from the ground up. Probably first by listing the things the combobox needs to accomplish. Think of it as an abstract object and not a specific implementation (a combobox is a specific implementation). Or you could 2) create generic combobox class and gradually add in the functionality you need, carefully testing as you go.

I think you'll be happier in the long run, and it will probably be easier to maintain, even if it seems like too much work in the short run.