Can't download SpringSource EBR bundles via Nexus although via plain mvn this works fine

Hey,
I know this seems to be an issue that reoccurs every now and then, but I seriously am not able to download anything from a proxied http://repository.springsource.com/maven/bundles/external/ nexus repo. I set up the repo 1:1 like my other proxy repos but still it seems as if Nexus is not querying the remote location. I can browse the remote SpringSource EBR from within Nexus but my build job returns "artefact not found", whether using -U or not. If I configure the EBR repo directly within my POM everything works fine, but proxying the EBR repo through my public Nexus repo group not.
I am really getting desperate. Any help is highly appreciated.
Best regards,
Oliver.

P.S.: I am using Sonatype Nexus™ 2.4.0-09