Mounting (sorry) behavior in dogs

[renegaderuby]

Neutered Colby is still trying to mount a Spayed Ruby? Ruby is the most "submissive" outta the WHOLE crew. And "colby" is the most submissive boy outta the boys.

Any ideas? Just trying to figure out why he's doing it. Dominance dosent seem likely because of the above listed reason. And it sure isnt hormones as they were taken eight months ago.

Side note,
toby (our currently unneutered) only shows intrest in our (currently) unspayed saydee. (yes they are both due to go in soon). so I'm really scrathing my head as to why a neuter is trying to mount a spayed. LOL