Thread:Feedback/Restoring deleted thread

I have created a thread Thread:Talk:Sandbox5/Read_a_letter_from_Jimmy_Wales_and_Michael_Snow., deleted it, created again, tried to restore deleted revision. Got error:

A database query syntax error has occurred. This may indicate a bug in the software. The last attempted database query was: (SQL query hidden) from within function "Thread::save". Database returned error "1062: Duplicate entry '144' for key 2 (10.0.6.21)".