I've had great luck w/ MecGars. CZ75, Tangfoglio Witness, DW .40S&W 1911. All excellent. MecGar probably made your factory mags. There might be some odd aberration. Call MecGar CS and see what they can do for you.
Greg USAF Retired NRA Life Member "If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." Milton Friedman
None of my CZ75B mags drop free, including the 3 factory mags. I believe the 75B at least, is designed that way. If you check out the CZ-USA website and read descriptions, a few models specify "drop-free magazine" which would lead me to believe that other models aren't supposed to drop free.
FWIW, the 3 Mec-Gar mags I have for my 75B are identical to the factory mags. I'm fairly certain the factory mags are made by Mec-Gar.
Mec-Gar (I wanna say they're somehow affiliated with Beretta) actually makes "factory" mags for a number of major names in the business...Sig, Beretta, CZ, some Browning and Ruger, and many others. Most of their "Mec-Gar" named mags are first rate and in my experience equal to factory mags.
In some cases (possibly when they don't fill the factory mag contract) they're not so hot. I've heard their 1911 mags aren't so great, for example. But I've run Mec-Gar mags almost exclusively in my CZ 75b, BHP, and Sig P226 with nothing short of perfect results. And they all drop free just fine for me, except in a couple cases where the mag was of slightly higher than typical capacity.