Created attachment 146902 [details]
Cell above the line has a border on the bottom, below on top
Introduced for 5.2 (https://wiki.documentfoundation.org/File:Adjacent_borders.png; see also the release notes) solving bug 34449 the adjacent cells should somehow collapse border lines set on two adjacent cells. It's unclear how that works and the UI gives no clue. And I don't see how the disabled control is enabled.
Build ID: 6.1.3-2
CPU threads: 8; OS: Linux 4.19; UI render: default; VCL: gtk3;
Locale: de-DE (en_US.UTF-8); Calc: group threaded
Rafael Lima committed a patch related to this issue.
It has been pushed to "master":
tdf#121613 Add information about Adjacent Cells