Binary package hint: plymouth
This bug only refers to issues with the text.so plugin; this plugin is used when there is no DRM or Framebuffer device available. You can recognise it because it says "Ubuntu 10.04" across the middle of the screen, rather than displaying an Ubuntu logo. If you see an issue with similar-sounding symptoms, but see the Ubuntu logo, please file a new bug.
So far occurances of bug has been due to the VT (shared by Plymouth and the X server) being reset by Plymouth back into Raw Mode after X has started and set the VT into Canonical Mode. I had believed I had eliminated the code paths that could do this, but there must still be one out there somewhere.
I've been able to replicate this on a slow-booting laptop only so far