I've cloned The "Function of Plate Glass" Window to create a prison window and I added an extra subset, made the new subset designmode enabled instead of the window glass, which I wasn't gonna use at all, but left in there because the object wouldn't work without it, so I just made it totally transparent!
The strange thing is as you can see on the picture, both my subsets can be designed when the window is placed on a straight wall, but when placed on a diagonal wall only 1 subset can be designed, however moving a designed window from the straight wall to a diagonal works perfectly, still the design tool just won't me the option to change the second subset until it's on a straight wall again!!

The original window which I used as a base for my clone does the same and so does a lot of other windows - not all though!

I'm a bit confused on why this happens so please help me out if you can!

You have only added the bars subset into the tsDesignModeEnabled block in one of the Geometric Nodes, with both the straight and diagonal window. You need to add it to both . And, since, the diagonal is borrowing its materials from the straight one, you also need to add a new string for the bars subset into tsMaterialsMeshName that links to the straight version.

I only added the bars into the tsMaterialsMeshName and then it worked!
Do I really have to add the bars into the south versions of the Geometric Nodes, the bars only exists in the north version of the GMDC?
It seems a bit odd to me that I have to add them to the south versions also, but I'll do it if you can give me a good reason

BTW Thanks for the speedy & working reply IB - Have a coke on my account

Oh, if the subset only exists in the south version, then you don't need to edit the north versions. Sorry, I didn't notice that.

It's allright IB, you did provide me with a solution, that's what counts - Thanks :D

BTW since my problem is solved, you may lock this thread!