Last night I participated in EMC's 4th birthday party. A big thanks to staff for putting it together. One of the drop items I received there was a +125% speed horse egg. Today I spawned the egg at my residence in town so I could use it for breeding purposes. I gave the horse some wheat and it instantly grew to full adult size with just one feeding. I then tried to ride the horse in order to place a saddle but it instantly reverted back to its smaller form. Nothing I do to try and tame the horse is successful. It just turns back into a foal again. I have never encountered this before so I am stumped.
It's a client-side bug. The horse isn't actually growing to full size, it just looks like it is. Feed the horse a stack or so of sugar and then ride it.
You need to feed the horse a whole stack of sugar or wheat without trying to ride it. When you try to ride it after a few feedings, it starts over as a baby. A whole stack will ensure that it is full grown and probably tame it as well. I have had this bug happen as well.
This happened to me when I was on 1.8 but EMC was still 1.7. You just have to feed it until it stops growing.
I will add now though that I waited for the horse to grow to full maturity on its own without feeding it anything and I can now tame it normally. It seems as PenguinDJ mentioned that the issue lies in trying to shortcut your way to full grown size by feeding it, not the taming process.
