Dude, I think just about anyone's juices will do that...
I've recently dealt with that out of some Atomic Cinnacide from Tasty Vapor. While the color hasn't changed, it has literally turned into something completely unvapable...And worse, it's killed every atty/carto I've put it in. I mean, said atty/carto could be functioning completely fine (as it was when I had the blueberry smoothie in it) and not too long after I put the A/C in it, I get barely any vapor out of it, no TH, yet the flavor's still there.
Now, I completely agree with you on the notion that juices change color/properties...My mom had some VB Green Apple I gave her, and it changed color, had a funky metallic taste to it as well. That said, she also had that same bottle of juice since I got her started a couple months ago.
Here's some food for thought: this effect only seems to happen with "fresh-made" custom juice, not commercial stuff like your Dekangs and what-not. That said, I can't help but wonder what they're putting in their juice that's making it keep. I dunno about you, but I think I'd much rather have some juice that goes bad in a couple months than to be vaping preservatives and not know it.
I honestly believe it's part of the natural process for juice, don't think there's anything these custom-juice vendors can do about it. Anyone else ever have something like this happen??