well it`s simply water that`s caused this, either you added a little too much at the start or the air humidity was too high where you let it cool.
I use Sesame oil to start my sugar off instead of water, and a very gentle heat, maple syrup or molasas will work also, but not too much, infact sugar will melt quite nicely on its own with the correct heating and will stay that way for a very long time before it starts to change color and caramelise. I don`t do the water test either, the Cold plate test or the back of a spoon (like you would with Jams) is a little more usefull I find.
I don`t know if that`s of any help to you or not, but it`s most likely the cause :)
as they say in Science "There`s no such thing as a failed experiment, only more data", and it`s doubley good if you can eat your data regardless ;)
So long and Thanks for all the Fish ;)