As discussed in T3250, key_mangling of tag node values is a problem: since key_mangling is globally applied, it will not preserve the form of values/names containing hyphens, causing an inability to recognize or evaluate said value. For example, in the case of T3250, local usernames containing hyphens will no longer be recognized by a pppoe-server.
Consequently, tag node values should be excluded from key mangling.
Note that, as discussed in that task, key_mangling will eventually be phased out; until then, workarounds such as this will be needed.