The regexes in https://github.com/jenkinsci/jenkins/blob/1d63adb1ce5bb56e8d06b004a5c78c432efe42e6/core/src/main/java/org/jenkins/ui/icon/IconSet.java#L93-L95 specifically exclude ampersand characters in attribute values for no apparent reason, resulting in improperly "reset" symbols if the attributes contain that value.