In TRAMP 2.5.0.1, the sshx and scpx methods were changed to use RemoteCommand for specifying, well, the remote command to run (see commit aaffd34492ea6168cc47c469799ac87aa5c052a9[1] for the actual change). However, this was specified as
RemoteCommand='%l', which fails on MS Windows systems since they only allow shell-quoting via double quotes.
I've confirmed locally that changing to double quotes, i.e. RemoteCommand="%l", makes everything work correctly. Obviously that isn't what you'd want on a *nix system, but even on MS Windows, I imagine this would fail for multihop cases (e.g. MS Windows -> Linux -> Linux). There might also be further issues with quoting if the %l placeholder is generated with sh-style quotes, but I haven't encountered any problems like that.
- Jim