Sorry for the title, I couldn't phrase it any other way :)

I posted a long time ago about Mason constantly being humped by other dogs, male and female, and was recommended that I have his anal glands checked. Well he has just had his MOT and all is fine in that department but the humping seems to be getting worse.
He is now 14 months old and not overly submissive, much prefering to have a play but it seems as though every other dog we meet while out just wants to hump him. It doesnt bother him so much (I think he likes the attention :) ) but it does bother me, and its making me wonder whether there is something else wrong? Ive lost count of how many people say "oh, well he's never done that before" while there dog is going for gold over my boy!
Has this ever occured with anyone else? If so, what was the reason? Id love to find out if anyone elses dogs are similar to mine, as of yet I've not met one!

Has he been castrated?  This is common with males that have been castrated, especially when young as their sexuality is ambiguous and it also lowers their status.

The reverse could be true if he is maturing sexually other dogs are seeing the need to keep him from getting too big for his boots.

Sorry, I forgot to add that he is entire as I have no reason to castrate him.

That is interesting, as it has been getting considerably worse with him reaching adolescence.