During long edits, there is a possibility that the session is closed, for multiple reasons:
1. Session timeout
2. Abrupt end of connection with server etc
In such cases, data typed may be lost.
Like in some other Wikis, enable periodic automatic save (1 min?) of the document which is being edited, save it as draft version without incrementing the version no.
When the same page is accesses next time, a warning should be given stating that a draft version exisits.This draft version should appear in the history.
The user can select the draft version and once he saves the document, the draft version is removed and the version is incremented.