Modifying bay or bow windows Architecture 2018

[s2009d]

Hello!

I've recently begun a new job and the system they have is Autocad Architecture 2018. My question relates to using bay or bow windows inserted with the tools palette. Whenever I insert these they seem to have a boundary in a thicker line that I can't seem to turn off or hide. I have attached a screengrab. the red arrows indicate the line in question. 

Ideally, I want to turn off / hide the line spanning between the walls (larger red arrow pointing upwards). When I insert casement windows they don't seem to have this thicker line on them. 

I have looked on the forum for hours but can't seem to find this question. Any help is appreciated! 

[R_Tweed]

The block used for the bowed and bay window have display overirides applied to the slabs used for the sill and ceiling. You will need to edit each and turn off the boundary as shown below.