Uploaded data not well formed

When I create a fresh Firefox profile and try to sync my library for the first time, I get the following error "Uploaded data not well formed".188BET靠谱吗This happens reproducibly, but only appears to happen on first sync and only when I leave the default Zotero item (Zotero Quick Start Guide) in the library before syncing.188BET靠谱吗This results in a conflict resolution window popping up, where I select the remote (deleted) object for both the Zotero item and the note attachment.

Report ID for the submitted report: 933078420
Report ID that appeared next to the error message: b869364222

Firefox 20.0.1
188BET靠谱吗Zotero 4.0.5
Windows 7

This also happens on the current HEAD of the 4.0 branch
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