If a new uid is added to an existing key, gpg should also adjust the key expiration time stored in the existing user ids. This would help in case some user ids are filtered out with --export-filter and thus modify the keys expiration date. The drawback is that additional self-signatures are required. It might be better not to do this in the general case (adduid command) but suggesting to change the expiration time only when needed.

In any case this needs to be fixed in gpg-wks-client.