Page rename crashed second time around

Just trying a few things in 2.5.108...only having recently switched from 
2.4 so this may not be recently introduced problem.

Did a page rename (updating referrers) which worked correctly first 
time, then I tried another one and it crashed with a servlet exception 
message to browser, null pointer in something to do with the lock 
manager? (This didn't appear to make it to the logs either).

Restarted the wiki, and the page rename had actually succeeded, but it 
crashed before it got to update the referrers.

Hopefully should be easy to reproduce?

Cheers,
Milt