Mystery solved
Like many of you, I purchased a box of these aftermarket retainers. I happened to purchase it from
http://www.clipsandfasteners.com but the part number and appearance of the part is exactly the same.
Like others have noticed, the part looks similar apart from the smooth finish compared to the grained finish of the OE part. However, they don't operate the same as the OE part, in that the center pin will not push in to unlock the retainer, making future removal a real b!tch to do.
Curious about the difference, I removed an OE retainer and removed the center pins from both the OE and aftermarket retainer. What I found was that the center pin of the OE part works perfectly with the body of the aftermarket part, but that the center pin of the aftermarket part did not work (ie did not push in to unlock) with the body of the OE part. Both parts looked identical, but when I measured the diameter of the head of the pin, I found that the OE part was just over 0.1mm smaller than the aftermarket part.
So, the solution is pretty simple and straightforward: file down the head of the center pin until it works properly. I did this with a flat metal file, and rotated the head of the pin against it. It took me less than 30sec per pin to do, and they now work as they should.
I also bought a box of Acura push-type cowl retainers, and those looked and functioned exactly as the OE part.