problem upgrading ubersvn with proxy

i have a problem upgrading ubersvn through a proxy server.
i configured proxy settings and the test button worked fine.
also it shows me that updates are available but downloading them fails with error message "File download failed: Connection timed out".
the proxy connection is working fine in browser and wget.
by the way i'm using version 12.3-9420 SVN - 1.6 running in a virtual machine with CentOS 6.2 x64

i tested with wget to download the following:
wget http://update.ec.us.ubersvn.com/uber...3153-2.tar.bz2
this was successfull.

the proxy server uses no authentication.

can someone help me?