Currently, LibActionButton-1.0 adjusts the text position of the HotKey region based on its value. This is behavior that the official client removed in 4.3.0 (15005).

This issue was reported here and compatibility code was implemented in Masque to account for it. As of 0.35-6-g8c96488-alpha, this issue has been addressed. (👍@Nevcairiel )