When renaming inline in a long file name in the icon mode, i.e. it is shown in several lines, pressing the up key sometimes does not move the cursor up. For example with: 7. abcdefg.HIJ.LmnO.[www.aaxa.com].txt when it is shown this way (icon with 80 pixels): 7. abcdefg.HIJ. LmnO.[www. aaxa.com].txt When F2 is pressed, it is shown: abcefg.HIJ.Lmn O. [www.aaxa.com]. when the UP key is pressed, it can't move beyond the "O." until I press the right key and then it can move up again.
I've just tested on several folders with very long (3 and 4 lines when split) filenames and cannot reproduce (Dolphin 20.08.1). Can you please re-test on a more recent version Jaime and confirm if this is still an issue for you.
I've been able to reproduce it only once in several attempts. Not as frequently as I remember. It works for me.