There is no difference at all between the covers that I have. The only thing I can figure out is that the contacts tabs on the inside of the covers that does not work, do not make a contact with the antenna that is embedded in the bothom plastic of the cover.
I do not know if the WiFi problem is related to this, (as I think the WiFi antenna is located in an other place on the cover) but for me the slow download speed I was getting before I change the cover, & the low signal or no signal was directly ralated to the lack of good antenna.
In order to come up with this solution, I went great lengths in order to find the right tab that was the antenna. I even install a temporary antenna (See immage) on the outside of the thone & I was getting better signal.
But after receiving my second Titan from AT&T online order I tried the cover from that secont Titan & Voila !! Very good service & signal.
Hope this help.