pm-update with --svnsync wipes svn folders/files

not a big drush user but the drupal update feature; although really cool, wipes out my svn files.. i seem to recall someone telling me drush wouldn't do this

but using this command:

drush --uri=http://boma.peter --svnsync --svncommit --svnmessage="test1" pm-update advanced_forum

wipes out my svn folder in the module folder (and of course therefore doesn't do any of the svn functions either).

i am not actually all that worried about having drush do my commit; but would be very handy if it didn't remove the .svn folders.