This is due to vBulletin 4 not being compatible with PHP 5.4. The only way to avoid it is to turn error reporting off, but we need that on the development site. I'm marking this as vBulletin Bug as the errors thrown are from vBulletin code, not VaultWiki code. I would advise against using the editor switch on the dev site.
I have already opened a report about this when ckEditor was implemented during summer 2011: if an error occurs during editor switch, the switch should fail elegantly, rather than eradicating the editor content. But it doesn't look like they heeded my advice.