Are Humble Store coupons stackable?

I dunno :(
Would be nice :)

It doesn't want to work for me either. I can see the "Select a coupon" box when it's in my cart but it doesn't seem to want to let me apply it.

Seem to remember actually using a coupon when a game was on sale at Humble Store before, but am not sure. I think I got Grim Fandango like that, and it let me stack the discounts. Will have a look through my email records and see if it shows anything. Will reply again in 5 minutes once I've checked.

Tried it with Just Cause 3 too, but worked neither.
Life is Strange should be $7.49 with coupon because the current price is $11.38, otherwise buying a coupon would be kinda hoax. They've never mention coupons aren't working during sales.

I really want to get this but with the 33% discount it's still more expensive than buying it at full price straight from Square Enix here in Australia. I remember the Borderlands Pre-Sequel coupon from the Borderlands bundle did stack with a sale price shortly after.

Btw since we are on the topic of stackable coupons, could I ask if steam coupons can stack with steam store discounts? (e.g can a $10 with 75% discount be stacked with a 75% coupon to make it $0.625? Or anything along those lines)

Similar to UraniumFalconPunch, I bought Grim Fandango (reg. $14.99) at 60% off (to $5.99) then was able to apply a 30% and 10% off coupon (to $3.77), both from E3 2015 Digital Ticket. Perhaps they changed it or it's getting confused with both discounts being 33%.

The answer I think is yes and no. At times they have been stack able for me, other times not

I recall something about them writing that coupons don't stack with any deals, they overwrite whatever percentage was originally on it (even if, for some reason, the sale would be cheaper). In any case, whenever I tried, it never stacked, so the empirical evidence shows a firm "no".