The little metal clip on the back of the pad along with the grease will help. I have no idea why. But I had the same problem with my fronts. I just put the pads in place and rode. Afterwards, I dug my old pads outta the trash, took the clips off, greased 'em up and no problems since.
2011 XR Midnight Cherry, Hard Bags, Vic htd grips & seat, Vic medium Windshield, unlocked speedo, Lloydz Air filter, VFC III, Lloydz ATS +4, Vance & Hines slip ons
1993 Vulcan 1500 (sold)
1981 Yamaha Seca 750 (ridden into oblivion)
1977 Honda 550 (sold)