I would say it is a bug.
You can probably get away with it in 3D due to the shading, but in elevation it is not good at all.
I was wondering if it was the type of rail or the profile but i just tried a few different option in a default template and the mitre lines never show.
Even where rails join into the round posts is not correct.
If anyone knows of a magic setting please let us know.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11