2D Board Game Movement Script Results in Empty Calculations

Okay, so I have a function that generates a list of possible moves one can make. From this function, tiles are overlaid with a blue highlight. When clicked, this highlight should move the selected character, provided there are no enemy characters on it, to the tile.

     void OnMouseOver() //Snippet from the Movement Highlight's attached script
     {
         print("Get off of me!");
         if(Input.GetMouseButtonUp(0) && !UIMan.UIActive) 
         //if we left-click and we aren't drawing any menus
         {
             print("!HERE!");
             if(overlaidOver.stoodOnBy == null) //if no character stands on this tile
             {
                 PersonThisBelongs.StandingOn.stoodOnBy = null; 
                 //the tile the selected character is standing on: no longer stood on

                 PersonThisBelongs.gameObject.transform.position = 
                 overlaidOver.gameObject.transform.position;
                 //set the character's position to that of the clicked-on highlight square

                 PersonThisBelongs.StandingOn = overlaidOver;
                 //the character is now standing on this tile

                 overlaidOver.stoodOnBy = PersonThisBelongs.gameObject;
                 //the tile is now stood on by the character

                 PersonThisBelongs.canMove = false;
                 //the character can no longer move this turn

                 GameMan.CloseEye(); //removes any pathfinding data and deselects the character
                 //Move the character to that tile
             }
             else if(!overlaidOver.stoodOnBy.GetComponent<Character>().team && 
              overlaidOver.stoodOnBy != PersonThisBelongs) 
               //if we are clicking on someone on our team
               //& they are not the one we have selected
             {
                 GameMan.CloseEye();
                 GameMan.TheEyeIsWatching(overlaidOver.stoodOnBy);
                 //call the deselection cleanup method
                 //select the new character
             }
         }
     }

UIActive is false, but we don't even reach the second print statement. Also, when a movement highlight square is clicked, the game drops to about 30 fps for a split second presumably doing calculations before spitting out nothing. The movement highlight, tiles they are over, and the characters all have 2d box colliders attached to them.

I can provide other snippets of code if they would be helpful, but this is the problem function at the moment.