And to add to Al's points he makes of using certain percentages of argon in the mix, here's an article that will back up what Al's talking about:
http://www.fabricatingandmetalworking.com/2013/10/percentage-of-argon-in-mixed-shielding-gas-does-matter/Even if one is using Metal cored filler, the same potential for these sort of problems can happen so one cannot say; "Well, that's just for FCAW dude!"
Your best bet is to heed to Al's advice about making sure what mix you can use with the specific cored filler you're using with the manufacturer of the wire & the EOR before moving forward and deciding to use it blindly.
Respectfully,
Henry