At the moment a remote client will ask for the xml files describing the variant from server only, if it's a variant different than the one which is currently loaded (e.g. during application startup, which is selected in the variant selection drop-down menu). This will cause problems if server side (especially the one hosted on public server) runs already a version with variant changes in it, but users use old clients.
The client will thus see e.g. different recruiting conditions, skill/power factor values, or whatever was changed. Either the client prevents actions which would be allowed now, or it allows things server will reject.
We have two variant changes pending now, due to which I didn't do a new release so far because of those compatibility issues above.
IMHO best solution would probably be, provide a new (minor bugfix-) release which brings a fix to only this problem (identifying itself as a new client-counter-version, from 4 to 5 I think), and before making a release that incorporates variant changes, make the "minimum accepted client counter version" also 5. And give players/users 1-3 weeks of time to upgrade when it suits them.
Partly fixed in trunk in r5243.
(WebClient side. WebServer side checking which version webclient is still missing).
As usual, leaving open until it's visible in an official released build.
Diff:
Fixed in r5243 - Remote clients now always freshly load the variant.
Leaving in state open-fixed til next release, as usual.