I have noticed that RichText/RichEdit gets quite slow in some cases, especially with long paragraphs.
Over weekend I have added some caching to RichText that completely fixed this issue; however I have had a hard time to get it right, it is quite tricky.
I hope it is fine now (no more crashes and arifacts), but if RichText starts to misbehave in new strange ways, you will know why and you will know you should tell me ASAP...