there 2 possibilities that why it can be happen,
1.You're executing the order but your account can not handle it,
for example :
you're closing your sell order and at the same time you're selling it again because you can see your balance in your account.
if you do that,you will get the problem.
2.You're executing the order with low fees and at the same time the network is very heavy.
my piece of advice as trader on etherdelta,always make sure about everything that you do.
always check your orders and never let it open and at the same time doubling it,because everything that you do in there,
you will be charged.
and never lowering the gas(standard if the network is heavy,but if everything is normal you can do it.
it is a decentralized exchange,everything that you do will be charged.
so make sure to check it before execute it
Thanks so much