I solve by hitting space key, not by clicking. But I think I got what causes it to increase > 10... It's probably caused by the way, I change the skin on the clicked tile. I create bmap and fill it with color each time I click (yes, it's an awful way to do this, I changed it, so now I create 4 bmaps right at the start of the engine, then change tile skin via ent_setskin, instead of creating them each time at run-time).

Thank you for the code man! Going to get into it right now