I'm doing WPF development with VS2010RC and the up-to-date EAP builds (1641 at the moment).
I'm seeing a problem which occurs after some time (an hour or so), where R# somehow seems to lose the association between XAML files and their code-behind. This causes lots of errors - errors in the XAML where for example event handlers are shown as errors, and errors in the code-behind, where references to objects created by the XAML are seen as errors.
The project compiles and runs fine, but of course the 'go to next error' feature in R# becomes useless because of all the false positives.
It doesn't happen to all files at the same time, and I'm not sure what triggers it - I suspect it starts with an error in XAML which I'm working on, which causes some kind of upset in R# which doesn't get recovered from once the file is fixed. There are no R# exceptions shown. Unloading and reloading the solution (you don't need to restart VS) fixes the problem, although the errors remain cached, and you have to 'visit' each file with a false error in it for R# to realise it's OK.
I'm not sure of the best way to report this kind of bug, or what supporting info you need. I tend to see this every hour or so of work, but that doesn't mean that it's going to be an easy repro for anyone else.
If anyone at JB wanted to do remote debug or needs a process dump, I can probably arrange that.