v1.07-1527 Mission Editor Phase Selection Button Unresponsive

[PandaShao]

Hello,
I am currently on version 1.07, build 1527, and I am experiencing an issue with the mission editor. To be specific, the dropdown selection box for "phase" is very "sticky". Whenever I try to switch between the phases, either "Waiting for Trigger" to "Triggered", or "Triggered" to "Satisfied", the dropdown list just close and the phase doesn't change.
I notice that, for example, when I try to switch from "Waiting for Trigger" to "Triggered", I hover the mouse over the "Triggered" choice, but the "Waiting for Trigger" is highlighted (see screenshot attached).
Could you please take a look at this? Thank you!
(Added a save file for Flight Tutorial one as an example, thanks!)

Edit:
If I try to click on "Triggered" for multiple times, maybe 5,6 times consecutively, eventually it will switch, but again, it's very "sticky".