Experiencing similar problems, I have the same errors as described here, ie.
INFO: No credentials available for BASIC 'GIT at CERNfirstname.lastname@example.org:443
having global and domain credentials defined.
Tried it with: Jgit, default git with distro (Scientific linux CERN 6 (basically SL6 / RHEL6), git 1.7.1) and also even locally compiled newest git 22.214.171.124 - nothing works. It works (eg. with .netrc) when used manually from command line on the same account but not working when executed from a Jenkins' job.
Also - version 1.4.0 is not working anymore with .netrc way of providing credentials for auth. (maybe not preferred but at least working...) - so I had to revert git-client plugin to 1.1.2 to make the jobs working again.
Concerning user experience - note that proper way of using credentials are kind of critical for usage of this plugin - for our case (and I guess for many others) the plugin is basically useless without it... Until it is working properly we will have to stick to old version with .netrc.
BTW. If there are some issues with 'credentials/whatever' plugin maybe providing possibility to set user/password directly just for GIT client could be a temporary solution (just to make possible overriding eventual issues introduced by credentials-plugin, of course not as suggested way of usage)...