I'll see if I can update this post later when I have some more time...
Here is the bottom line - there are no high speed cables in the 15 meter (~45 foot) range. So, shockingly, what you got from ebay is likely a couterfeit cable. I'll have to go through this forum's archives but I remember a few threads discussing problems with that "brand" of ebay purchased cables.
So, my suggestion is to take advantage of their 60-day no questions asked return policy and then purchase from a reputable place. I know you're pretty far away from the U.S. but look at the monoprice and blue jeans cable websites for an idea of pricing. For a high speed cable you should always be able to ask for the manufacturer's high speed certificate for that length of cable (not a shorter cable length).
You did the right thing by testing before you put the cable in-wall. Keep in mind that high speed is limited to about 25' (a little over 3m). More information at this thread (please ignore the "garbage" in the middle of the thread).
Your question about why the cable worked with only 2 of 3 montors is because you are outside of the HDMI spec at that distance and for the type of signal you are sending. If you sent a 1080i or 720p signal, the projector might work, as well because you would be back within spec for 1080i/720p. If it didn't work, I'd suspect the cable is defective (as well as counterfeit based on the ebay description).