Levelling up minigame needs elite mouse-clicking skills

I ran my first Elemental game, as Procipinee.

I have researched fire dart, and bring with me Muvueratha the worthless, who has a dagger and attack 4.

We solve a quest (read, I kill 2 goblinoid creatures with fire darts).

We then attack a wolf, which we (read, Procipinee alone again) kill too.

I may have selected Muvueratha at that time. Or clicked somewhere in the tactical battle window. Not sure, as the screen changed fast:

We got the level up stuff.

Normal screen, and Muvueratha asks to gain one level with all the + options. . Unfortunately, I can't click anywhere to any effect. The mouse icon is a cross with the path, something like that: (sorry, screen captures leave the mouse icon out so I had to draw it).

Result: I can't click on any +, nor on OK which is greyed. Or so I think.

I am stuck, and think it's game over, but I insist. I know I managed to get a tooltip under one of the attributes, so maybe I can do something. After a lot of experimenting, I finally managed to hit a plus sign and increase an attribute. It looks like if I find the right pixel on the upper left of the mouse cursor and put it exactly on the center of the + box, it's possible to select it.

However, I must say this minigame of 'find the pixel' is rather irritating. Even after I managed to get the + sign for Muvueratha, I had to click 4 times for  Procipinee before managing to hit the right mark. Maybe doubling the size of the +/-boxes could help?

Or make sure the icon doesn't turn into/remain in movement icon shape once the battle is over?

It's repeatable after every fight