Strange boundary for postal_code = 1301

I was looking at boundary=postal_code in Walloon Brabant in overpass turbo and I was surprised to see that while the boundaries are perfectly interlocking, the one for postal_code = 1301 (Relation: 13533592 | OpenStreetMap) is strangely not matching the boundaries of its neighbours, leaving gaps and overlaps (see screenshot below).

Then I found out that there is actually a relation that perfectly matches the footprint left by the neighbours: Relation: ‪Bierges‬ (‪11064061‬) | OpenStreetMap but it is tagged differently with adminlevel=9 and wikidata and wikipedia references.

I guess I am confused as to why there are 2 different boundaries with postal_code = 1301 and I am wondering if something does not need to be corrected there.

It looks like something went wrong since the postal code of Bierges was modified as it has its own code (1301). Limal on the other hand which also belongs to Wavre has the same code as Wavre. I hope Pieter reads this post. He might know how to fix this. I also notice that some areas in Wallonia are not done yet.

Thanks for reporting this!
Weird shape indeed. Usually admin 9 and postal code boundaries coincide, though not always. I’ve removed the weird shape, and created a duplicate of the admin 9 area with just postal code tags. See Changeset: 143413341 | OpenStreetMap