1. Place a AT Mine or any other.
2. Try to add an Eventhandler to the mine with: (cursor is pointed at mine)

cursorobject addEventHandler ["Killed", {diag_log "!!!Works!!!"}];

3. Get the return of -1 which is not even documentated on https://community.bistudio.com/wiki/addEventHandler

4. It is the same for addMPeventhandler.

I am working on a Database also for Mines which have to update if Mine is picked(EH deleted) up or Exploded(EH killed). Without a working Eventhandler it gets somewhat frustrating to do it properly.

I am not sure if this is intended or not.

I am using right now:

[_mine] spawn {params ["_mine"]; waituntil {sleep 1; not alive _mine};systemchat "DEAD";};

to check if they are picked up or deleted. So it seems like the main function is here, but it is not possible to add event handlers.

If it is a bug you might want to consider to make own Eventhandlers for mines instead of existing one if they make sense. Like:
Mine_exploded
Mine_disarmed

I would personally classify it as a block because you can't do scripting like intended with this issue.
Please correct it if this is not the right severity. I was pending between minor block an major. Minor seemed to innocent for this, major to hard and block seemed right because it blocks a intended function.