That looks to be either a limitatin or a bug.
I suggest you submit that as an ER.
I tried and was able to break the lines in an Isometric view. Can you post your model and drawing here for someone to check? Click on "Use advanced editor" at top right to post files. Please Pack and Go the drawing to a zip file and post that.
Edit: I just tried again and can't get it to work. I didn't save the drawing I was experimenting with yesterday so I have no idea why it worked then but won't now.