If you are still using MQTT 1 you can use a REGEX filter to ignore those messages for that Item. In MQTT2 you can chain transformations and similarly filter out those messages by first applying a REGEX. See MQTT 2.5 M1+ How to implement the equivalent to MQTT1 REGEX filters.
It’s been out since OH 2.4 (nearly two years now). If you find it lacking, Issues are a great way to bring the need to the developer’s attention.