Sealing the gap behind the architraves?

i understand that architraves are primaril there to cover the edge between the plaster and the door frame. In pulling apart the newest door frames in the house, a couple of years old, I noticed that there was what looked like clear packing tape 'sealing' the gap behind the architraves between the door frame and the plaster. The older doorways, mid 90s construction, didn't have anything behind the arcs like all the others I have seen in older constructions.

Apparently the first owners of the house let it go and there was a vermin problem when the next mob moved in and renovated, including the doorway work so I thought it may have been sealed up to stop cockroaches etc getting in via the gaps. There may be another reason for the tape.

Thoughts appreciated. Is it a new standard practice, or an oddball attempt to stop the roaches invading? We've seen plenty of the six legged critters since moving in but seems to have backed off a bit and wondered if I should be sealing up the gaps to help keep them out.


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