My understanding is this is typically due to the latch clip spring being worn. Many people replace the latch clip and the latch clip spring as a set to solve this problem. I have also heard that if you pull the spring out and stretch it so its 1/8 to 3/32 inch longer...it will fix the problem for a while (eventually the spring will return to its original length).
While I have never personally had this problem with my M1, I have spoken to people who say this is a somewhat common problem. The spring and latch simply wear out.
While I have never personally had this problem with my M1, I have spoken to people who say this is a somewhat common problem. The spring and latch simply wear out.