This is the intentional reason why i subscribed to this forum.

I encountered a strange behave of the keymapper function of DOS Box in Win10.
Nothing serious it just acts sluggish, it won't open proper after pressing Ctrl-F1 and shows an empty black shell, after clicking randomly on any (still invisible) button in it it will display the buttons. If i like to assign a button i have to click 3 or 4 times on "Add", it shows off that it is ready to receive input but won't respond to the controller input before i press it again a couple of times.
(double clicking, but sometimes this even fails and i have to double click it again)

This results in multiple entries in the mapperfile for this setting i.e.
<key_esc "stick_0 button 8" "stick_0 button 8" "stick_0 button 8" "key 27">

I didn't used the mapper often and started to use it on my old Win-XP where it didn't showed this behave, but i like the mapper it's very handy if you have many dos-games which use only keystrokes as input. Of course other profilers as what comes with the hardware or X-Padder are more comfortable but i like to have the mappings hidden and not in a profiler.

recently i use it to create a basic mapping and edit the file because of the sluggish behave.

I hope this will help somewhat, i really like the mapper, for a long time i never used it because i feared it's complicated BUT it's very easy and quite comprehensible that's why i recommend to use it.