This commit https://github.com/openssh/openssh-portable/commit/7acefbbcbeab725420ea07397ae35992f505f702 Removed the feature that you could use the format -L a/b/c etc.. (this is used by http://sourceforge.net/projects/pacmanager/) basically hpdelim split on '/' - but parse_fwd_field uses that to indicate something else. As far as I could see the commit and "Potentially-incompatible changes" in the release log did not mention the change. was it an intended change? (I've no idea why PAC decided to use that syntax...)
The "alternative" host/port syntax was added in 2001: https://anongit.mindrot.org/openssh.git/commit/?id=62c25a43dbdd0dddb872b997a6f82b4f73c79180 and removed from the documentation in 2010 (with a comment saying it no longer worked at the time) because it had been superceded by [addr]:port which had become more or less standard by then: https://anongit.mindrot.org/openssh.git/commit/?id=7fa96602e52f02e66897f98a1568cbd3a555192b It was only ever documented as working for IPv6 addresses, though. So I guess this would be classed as "unintentional change of undocumented behaviour". I don't think we can make it work again without breaking Unix domain socket forwarding, though, so I don't think there's anything we can do at this point.
Set all RESOLVED bugs to CLOSED with release of OpenSSH 7.1