I know this thread is nearly a year old, but I wanted to post my answer to my own problem in hopes that it helps someone else in the future. So please don't bombard me with thread necromancy.

As it turns out the problem is in the setHtml method and the fact it is occurring within a threaded method. The setHtml method cannot operate outside of the Main GUI thread, so in order for me to post the correct HTML I need to use signals and slots. All is working much better now and I hope to use WebKit as a strong platform for my rich text chat box.