An amp should never backfeed into a remote wire period, if it does then its got internal failure. Futher to that the remote wire should be wired to the deck not a fuse block unless there is a reason for it. Using a proper fuse tap like bussman's BP/HHH is the safest and best means of tapping into a fuse block. I would never run a remote wire into ign source unless it had a blocking diode or a fuse in it to protect that circuit, you can burn up wires pretty easily if they are not protected and if the amp is feeding back into the remote wire that wire is not protected nor is whatever it is hooking into including the harness you tied into. I would be checking into the remote wire make sure it can not touch of the + feed wire for the amp and that they are well seperated. Fuse that wire at the amp if its going to be an issue with an inline fuse soldered in place and a 5 amp fuse.