I did some searching around on the net and read that intermediate filter drivers like winpkfilter can break things like wake-on-lan.
Can you give some links on what you have found? Basically IM driver can break wake-on-lan if you want to do so, but WinpkFilter does not try to do it on purpose 8)
Also, is there any WinpkFilter application running when you go into standby? If there is then breaking wake-on-lan is possible because no packets can be processed by application which does not get any processor time.