Convertible rear window tack strip and staples

[GTamas]

For some reason the staples holding the top of the rear window started falling out from the tack strip now for the second time in 3 months. Any idea why that's happening? First time it fell out in April and those staples were holding for 15 years when the factory top was replaced. Then i fixed it with new stainless 6mm staples into the old factory tack strip. Now they fell out again.
Could be the tack strip material got old and not holding staples well enough? Or should I use different staples?

 

[Slice]

6mm may be too long. All I could find in my area for stainless Staples were 1/4 inch and I could see they were too long. The points would bottom out in the tack strip and I could see underneath the staple mating point so I had to hammer them down individually. I suspect the staples at the factory are some special non-consumer item being stainless and maybe only 3 - 4 mm deep at the most. They might even have barbed/ringed edges to prevent them from pulling out. Another possibility is that the top is set too tight and pulling the Staples out.

Good move using stainless staples - regular staples would have rotted and the top come loose.