If I run xrandr --prop, I see this:

	scaling mode: None
		supported: None, Full, Center, Full aspect

Note that the value start with an upper-case letter. If I try to set the value with invalid casing, no error is printed out, but the scaling mode is not set accordingly. For example:

$ xrandr --output DisplayPort-0 --set "scaling mode" center
$ xrandr --prop

	scaling mode: center
		supported: None, Full, Center, Full aspect

It *seems* like the new mode applied, but in fact, it is still "None". That is very confusing for people, as you can see for example in bug 80868 comment 17 to 19. It confused me as well in the beginning, because I also first tried to set the values all in lowercase, but fortunately I realized the modes could be case-sensitive and found out that it really makes a difference.

In order to make this functionality better usable and mistake-free, please consider one of this solutions:

a) make the values case-insensitive, so "center", "Center" and "CeNtEr" would all set Center mode correctly

- OR -

b) print out a warning/error about invalid mode name when a person tries to set a wrong-case mode name. Also, do not show this invalid mode name as the current mode. So:

$ xrandr --output DisplayPort-0 --set "scaling mode" center
ERROR: Unknown "scaling mode" value "center". Supported modes are: <...>. Please note mode names are case sensitive.

$ xrandr --prop
	scaling mode: None           <---- not replaced by invalid value "center"
		supported: None, Full, Center, Full aspect


Thank you.

xorg-x11-server-utils-7.7-17.fc23.x86_64