There are several keys where it is not appropriate that multiple values should be mentioned, separated by semicolons. This often appears when several way segments with identical keys but different values are merged.
Best example I found so far: maxspeed=90;␣90;␣90;␣90;␣50;␣90;␣90;␣90;␣90 -> https://www.osm.org/way/217853059/history
Keys which should be checked (incomplete list):
See also my recent diary entry: http://www.osm.org/user/malenki/diary/21081
I implemented it as a new check for "suspicious values".
More suggestions of keys to check for (suggested by stw1701):
I'm not sure about the postal code - many big companies in Germany have their own code, but can also be reached by the normal area code. Maybe someone wants to tag both?
trail_visibility and smoothness are used very often with free text values - wouldn't it make sense to allow lists here?
You're right. I added the exceptions you mentioned.
I think we forgot to close this...
I cannot find "suspicious values" on http://keepright.ipax.at/report_map.php
Keepright.at is still not running on this version of the code - reasons are various, and it most likely will take a while until we do this step.