I agree that the 2D drafting functionality need to be enhanced. As noted here I think AC has some unrealised potential when it comes to linework. To me AC seems to keep good track of the lines but as a users I am limited in what to do with them.
The example you show is interesting and is somewhat related to what I discussed. The "floating" line is the coincidence of the line pen in the roofs composite separator and the line pen in the walls skin.
It turns out that if you set the line pen for the skin to a thickness larger than that of the separator then the skin will have priority - breaking the separator, creating a thicker segment. Similar is true if you don't have a separator. If you instead set the the line pen for the skin to a thickness smaller or equal to that of the separator then the separator will have priority - remaning intact.
This seem a bit strange and perhaps something for @Minh Nguyen to look into? Surely the default should be that the separator line pen has priority regardless of the thickness of skin line pen?
Yes you are right, the thicker line will get a priority, which very often creates this kind of unwanted behaviour. I beleive Archicad should either give you option to set custom pen for end segment of each material in a sandwich or at least a chekbox that would reverse this behaviour, as more often than not, it will result in incorrect display. Also the fact that the same pen is used when certain material is itersected by a material with higher priority and when it is inerupted by say window/door opening, creates a need for a lot of unnecessary workarounds. (actually the only situation when this default setting works for me is when I have a sandwitch with an air gap and then it displays it correctly) This I belive should be on top of the agenda to improve as there are whole markets where Archicad users have to choose either to deliver documentation that is not up to code, or to do manual drafting that by its nature adds tim (and cost) and more importantly can result in erros due to nature of the job.
From Archicad 8.5 all the way to the present. Passionate Autocad hater as well. Wish to save palets and menus individualy in work enviroments: https://bit.ly/3pg3Bx7
if you color just the end of the wall with a "material - Cut Lines" pen (eg. pen 143) you risk to have wrong representation in floor plan and near windows;
if you color those end wall lines with a "Element - Cut Structural" pen (eg pen 27) you can be pretty sure that sections (along intersection between walls and Slabs/Roofs) will be wrong:
The fastest way (in my opinion) to solve this problem, is to add the possibility to override just certain categories of lines (because for some strange reasons AC does something similar while exporting DWG files with some settings, so I suppose that it's possible even when we create Graphic Overrides).