Also, part of loading your pistol should be to insure that the magazine is fully inserted... to include pulling on the base plate. You found your problem and corrected it. Testing your gear is very important.
I've had pistol combos where the fully-loaded magazine would not seat properly with the slide forward, necessitating magazine -1, or just inserting the magazine and loading the top round leaving the capacity less one condition.
I had a Springfield 1911 that would not allow an 8-round magazine to seat fully and I've seen some of the 1911 mags do that with the PM-45 and P-45... allowing no increase in capacity over the stock flush-fitting mags.
That's something you need to know before a failed reload in a gun fight for your life. +1 carry needs to be tested with your magazine reloads, too.
USAF Retired '88, NRA Life Member. Wife USAF Retired '96
Avatar: Wynn re-enlists his wife Desiree, circa 1988 Loring AFB, ME. 42nd BMW, Heavy (SAC) B-52G's
Frédéric Bastiat’s essay, The Law: http://mises.org/books/thelaw.pdf
Thomas Jefferson said
“A government big enough to give you everything you want, is strong enough to take everything you have.”
and
"Peace is that brief glorious moment in history when everybody stands around reloading".