svn 1.7: how to recover from a lost pristine file

For some reason, I lost a pristine file [*] in a 1.7 working copy. I'm
trying to recover from this without having to throw away my entire
working copy. So far I'm unsuccessful. Any help is appreciated.

svn-1.7 is SlikSVN 1.7.4 (On Windows 7, 64bit):
[[[
C:\Work\WC-root>svn-1.7 update -r0 the\file\with\missing\pristine.java
svn: E155037: Previous operation has not finished; run 'cleanup' if it
was interrupted

C:\Work\WC-root>svn-1.7 cleanup the\file\with\missing
svn: E155004: Working copy 'C:\Work\WC-root\the\file\with\missing' locked.
svn: E155004: 'C:\Work\WC-root' is already locked.
svn: E155037: Previous operation has not finished; run 'cleanup' if it
was interrupted
svn: run 'svn cleanup' to remove locks (type 'svn help cleanup' for details)

C:\Work\WC-root>svn-1.7 cleanup
svn: E720002: Can't open file
'C:\Work\WC-root\.svn\pristine\6d\6d6e0892990e945b03a15b8e518dbef26848dc75.svn-base':
The system cannot find the file specified.
]]]

(the fact that the working copy is locked to begin with, was because a
normal 'svn update' failed because of the missing pristine, with "svn:
E155004: There are unfinished work items in 'C:\Work\WC-root'; run
'svn cleanup' first.", which is why I first found out about the
problem)

Anything I can do to investigate further?

Any repair actions I can take? The only thing I can think of is
checkout out C:\Work\WC-root\the\file\with\missing in a new working
copy, and copying the pristine file from there to my corrupted
pristine store.

[*] The pristine got lost after trying out a 'case-only' rename
through IntelliJ (Java IDE), which uses svnkit 1.7.4 snapshot version
r9054_v20120321_1804 (which should support this usecase). So that may
be another issue in svnkit, or in the way IntelliJ drives it (or some
random accident because I'm experimenting a bit too much with
pre-release software). It's too early to tell right now. Regardless,
it would be interesting to know what to do when a pristine gets lost
...

-- 
Johan