Wyatt,
At first I could not reproduce this issue on 2.5, 2.6 or our 2.7 development branch. I took a look at our templates and could see that the URL's were not properly escaped. So I was at a loss to explain what was happening.
I eventually managed to reproduce this issue against an internal server of ours which was using a HTTPS reverse proxy. It's possible the issue was affected by the HTTPS reverse proxy configuration (which is why I could not reproduce on the HTTP servers).
I have patched the templates to escape the URL which should address this particular situation. I will close this issue after I've seen it working via HTTPS.
Cheers
Matt
Fix is verified on our internal SSL server (extranet).
I've attached a patch for this issue. It will also be fixed in Confluence 2.6.1, which is due to be released in approximately two weeks.
This patch is based off the source, so you'll need to use patch's -p option to remove the leading paths down to just template/includes/macros.vm.