This has been going on a very long time. I need to double check whether it is SUSE only or everywhere, but I just uploaded a log for another thread that comprises an example of the problem on openSUSE 15.3. At some point from what is copied for pasting, a few additional space characters are appended to line starts, in addition to as many as were copied to the previous line. The result is line lengths well into triple digits, most of which are spaces but possibly some tabs. The example https://paste.opensuse.org/18808537 has lots of lines in the 400s where no such line lengths were present in Konsole.
To reproduce: 1-configure Konsole with more columns and rows than default 2-select considerable number of lines from Konsole shell window 3-copy 4-in next Konsole tab running MC, open some .txt file for editing with F4 5-paste
result: line ends move farther and farther to the right with each line from some random point advancing down being padded by extra space characters from nowhere.
I typically have my Konsole windows set to a default of 132x43 size, using font size inherited from desktop font settings for monospace of size 10.