why are parallel drivers bad?

I have been working on replacing a broken proprietary stepper driver with an arduino and some L298N dual H-bridge boards (available for $5 or less on ebay) and they do work when used individually.
However, when I wired two in parallel so I could deliver more current the setup just sorta vibrated like it didn't have enough voltage, and got very hot when driven at 12v. I eventually tried 35 and fried both.

So here's the question why do they get tweaked out when paired? The L298N boards are very dumb hardly more than the dual H-bridge with diodes, if triggered together I thought they would act as parallel transistors and share current load but this is obviously not the case. Any ideas?

seriously?
does any one know why drivers would have problems operating in parallel?
has anyone successfully run parallel drivers? if so how?

try connecting them in parallel through an inductor, this will take care of the shoot through current caused by timing differences
however, they should not get warm if there is no movment on the motor.. this implies it was wired wrong.
do you have an oscope to verify proper operation?