Samsung Monitor hijacking my keyboard maestro shortcut

I have disabled the default keyboard shortcut in System Preferences--> Keyboard--> Shortcuts--> Display that maps F14 and F15 to changing screen brightness. Instead, I have used Keyboard Maestro to remap F14 and F15 to keyboard triggers (CMD+"+" zoom-in and CMD+"-" zoom-out). This works as expected on my iMac 27 display, but when I moved the Safari window to the external monitor (Samsung U28E590), F14/F15 reverts back to changing screen brightness.

I initially thought my keyboard maestro was not working until I moved the safari window back to the iMac display. Has anyone else encountered this issue before, and is there a fix?

1: Use a different key as a short term fix i.e. not f14 nor f15 (i use cmd+ or - for mine)
2:Does the same problem occur with other programs e.g. textedit or google chrome?
3: Suspect you have also got a Samsung utility program that is intercepting the keystrokes.

Using a different keyboard shortcut will not help me identify the issue. This issue also occurs on Chrome and Text Edit, so it appears to be a system wide issue. I did not install any software when I connected the monitor, so I do not believe it's due to a Samsung utility program.