Main CCW (Makarov PM) fired automatically twice in a row at the range today

Before I get down to business, I'll give y'all a little bit of background. I carry a 9x18 Makarov PM with 8+1 made by the Soviets in the 90's. Ive previously put a few hundred rounds through it before carrying it and not a single failure to feed. I've been carrying for the last month and a half legally but only just turned 21 and was able to buy more ammo at the store without dragging a friend along. I've also just been paid, so I was able to go out and get all the ammo I needed.Since starting to carry, I've left my pistol in its holster sitting out on my nightstand. I always leave the fan running and the combination of a well oiled gun and the dust from the apartment had been making for a dusty gun every morning. I really do mean it was filthy. So I started covering it with a handkerchief to protect it at night and gave it a clean. Now, I wanted to know how it would fair at the range, knowing that Makarovs are real Soviet troopers, so while I've bee going out and drinking since I turned 21, I've left it on the table collecting dust each night. Spinning the magazine you could literally feel the gritty dust grinding on the sides.So, I took her to the range today and emptied that magazine. It fired 7 rounds fine, but the eight round got stuck in the slide after ejecting. I thought "that was odd, but that ammo was filthy anyway. Better keep it clean, duh!" I reloaded the magazine and gave it to my sister,who I intended on teaching to shoot today. I had gone over gun safety with her on the drive to the range and loaded up a single shot in the magazine for her first few rounds down range. It shot fine like I would have expected. I loaded a full magazine and handed her the gun again. When she heard the trigger I heard a Blouch! Blouch! and one round hit the target and the other hit the cement roof. She was still aiming downrange with her finger pulling the trigger all the way back. I took the gun and unloaded it while I tried to think of what to do. Later I realized that (with the safety on) the trigger pulls a hell of a lot more than it did two years ago when I got the gun. It's supposed to be impossible to pull the trigger or operate anything with the safety engaged.My question is, what happened? It's not safe as a CCW in its current state, is it? Can I replace some internals to get it back to a safe state? Was it something my sister who is new to firearms accidentally did? I doubt that last bit. Any tips are much appreciated! via /r/CCW http://ift.tt/2u8lRJJ