I have been able to reproduce this bug on r108.2
1) Create an empty project
2) On the event sheet, create a global constant
3) Create a global variable
4) Create any event and add to it an action to set the variable's value.
5) Edit that action.
Expected: the edit action window should show the action's variable and the value to be set.
Obtained: no variable is initially selected from the drop down list.
This gets particularly annoying when you have to edit the action often.