Strange gap above ceiling moldings.

[alm82]

Hi!

I have what I think are strange gaps above all the ceiling moldings in the rooms.
In the gap, you can see some hard dark blue material.

The house is from '65 and the ceiling consists of some type of fabric?

What could it be? Function??

 

[bonnier]

Shadow list, that's probably how it should look

 

[Stefan N]

Yes, that's how it's supposed to be.