I've completed this quest twice since you posted and got the reward everytime. I suggest screen shotting everything. As in your quest - the horse - and the lack of bubble pop up.

Ok I have screen shots can someone tell me how to get them on here?

You can upload them on an image hosting site such as lensdump, then you copy the image url. In the text editor here you need to click on Insert -> Image and paste the url there.

Both of those horses were captured before the date on the screenshot showing the double premium quest. This doesn't prove or disprove anything, as you could have captured those horses on the 8th and 20th before the quest popped up on the 21st. Quests do repeat, so maybe you have completed it and you're getting it again? I'm not saying this isn't a bug, just saying this can't prove it is indeed a bug. And don't give up on the entire game because of one quest. They are such a small part of the game experience.

I have on my side acc a quest for a few years now that just won't finalise no matter what I do, its stuck on it and that's it, I simply gave up and ignore it now. I keep doing all other fun stuff :)

I understand for you it is a small part of the game, for me it is why I play. I enjoy the quest's it is my relaxation, I don't play the game to be competitive. This post has been active on this situation for 4 months and a minimum of 4 horses that have completed the quest (but I really believe it is 5), I am sorry I did not screenshot the quest at the beginning but I really thought it would be easily resolved. At this point I don't care so much about receiving the "prize" as clearing the quest so I can move on to the next one. I will continue to post screenshots as I believe it is a glitch and should be resolved, but it is frustrating to be doubted about the dates etc. when this post has been in existance for so long.

And again it happens