"svn up -r" sometimes removes externals

Hi,

Today I tried to update a custom OFBiz working copy to a specific revision and got this

C:\********>svn up -r1634839
Mise à jour de '.' :
  U hot-deploy
Removed external 'hot-deploy\core'
Removed external 'hot-deploy\****po'
Left local modifications as 'hot-deploy\***po'
Removed external 'hot-deploy\********-theme'
Removed external 'hot-deploy\********hh'
Removed external 'hot-deploy\********comlead'
Removed external 'hot-deploy\********accnt'
Removed external 'hot-deploy\********common'
Left local modifications as 'hot-deploy\********common'
Removed external 'hot-deploy\productconfig'
Left local modifications as 'hot-deploy\productconfig'
Actualisé à la révision 1634839.

C:\********>

So it removed most of my externals, but not all.
I have 12 externals from 2 different repos (from ASF-OFBiz) .
4 remains untouched, 2 are from the different repos, si it does not depend on the repo.
3 are left with only their build folder
The others are totally removed

Weirdly, just before, I did the same with another copy I did some days ago which was not up to date (the above was already updated at r1634839) and
got not problems

Anybody an idea (did not find anything clear in Google)?

Thanks

Jacques
PS:
C:\********>svn --version
svn, version 1.8.11 (r1643975)
    compiled Dec 17 2014, 21:04:03 on x86-microsoft-windows

It's SlikSvn
Received on 2015-02-10 12:04:30 CET