How to troubleshoot "bzr: ERROR: Failed to rename"?

I tried to pull new changes today from lp:leo-editor, been a couple of weeks since the last time, and get this error:

{{{
bzr: ERROR: Failed to rename B:/apps/leo-editor/.bzr/checkout/limbo/new-189 to B
:/apps/leo-editor/leo/plugins/pretty_print.py: [Error 32] The process cannot acc
ess the file because it is being used by another process
}}}

I ran `bzr check`, which found nothing wrong.

SysInternal's Process Explorer does not find any process using that file. (http://technet.microsoft.com/en-gb/sysinternals/bb896653.aspx)

I then ran `bzr update`, which worked for a time and then failed to rename again:

{{{
bzr: ERROR: Failed to rename B:/apps/leo-editor/.bzr/checkout/limbo/new-143 to B
:/apps/leo-editor/leo/plugins/templates.py: [Error 32] The process cannot access
 the file because it is being used by another process
}}}

Finally after a second update everything seemed to work okay. What is causing these errors and is there anything I can do about it?

{{{
>bzr --version
Bazaar (bzr) 2.2.0
  Python interpreter: C:\Program Files (x86)\Bazaar\python26.dll 2.6.4
  Python standard library: C:\Program Files (x86)\Bazaar\lib\library.zip
  Platform: Windows-post2008Server-6.1.7600
  bzrlib: C:\Program Files (x86)\Bazaar\lib\library.zip\bzrlib
  Bazaar configuration: C:\Users\mhwilkie\AppData\Roaming\bazaar\2.0
  Bazaar log file: D:\Docs\Matt\.bzr.log
}}}

Windows 7 Pro x64