LOS Creation Issues When Trimming

[LordEntrails]

So am I doing something 'wrong' or poorly? Or is this an FGU issue?

So, when I'm creating LOS I find that very often deleting a node on a segment does not work as intended. Take this map (Thalivar's Beacon from Divine Contention). I have gone and done the walls and now am coming back and have put in the doors. Then to trim out the walls I do a small wall inside the door. Like this;
40183

Then I go to the selection tool, draw a box around the line and nodes inside the door rectangle. And about 10% of the time I get this;
40184

Sometimes I also find that it removes the cutting node, but does not remove the wall I cut (and actually removes the node).

Sometime I can undo it and redraw the cutting node and it works, but usually when it starts doing this I can't get it within 3-4 tries and I give up and start again.

Attaching the campaign file.

[spoonhead]

I’ve only been able to solve this by drawing in the doors, windows etc first, and then doing the walls. I then only go into the door with the wall, rather than out the other side. I can then delete the wall section inside the door. That seems to work for me.