AVG and Avast share the same core, but they have a different front-end ever since Avast bought AVG. I'm speechless, 'cause the UI used by Avast is just a C++ front-end compiled with SSE2 assembly optimisations targeting XP as well and it shouldn't have anything fancy inside. It should be slow-ish (on some systems) and not scalable (which makes it difficult to use on low res systems) but it shouldn't break. Besides, even if the UI doesn't work for whatever reason, the core and the protection engine should as they take the configuration from the configuration files and only the final integrity check should misbehave. In other words, the worst case scenario I was thinking about is the UI process using up all your resources trying to load itself up.
The worst thing is that I can't reproduce it neither on my computer nor on a VM.
Do you have Skype? Can you add me? (francebb1 - franceopf@gmail.com).
On one hand, I'd like to find out more about the issue in order to solve it once and for all, on the other, since I no longer have any affiliation with Avast and AVG shares its protection engine, I would tell you: "if it works, leave it as it is".
It's up to you; if you are willing to test a few other things (unofficially), add me on Skype and I'll add you to our group chat. (Dibya, Peter, Samuel... we are all there).