It's only a issue with the size of the splitter (1px). I'll increased ...
I'm used to resizing the Kune Inbox left column (the index of waves) when I'm scanning the wave titles (to see more words). I can resize it in Firefox but now I realised I cannot in Chromium (v18, Ubuntu 12.04).
PS: I don't remember if I could before the Breadcrumbs change. It might be related (?)