[ic] item-discount-subtotal not working for 2 or more

[Joshua Lavin]

My shopping cart is not displaying correct extended prices when using 
discounts. It works fine as long as the quantity is 1, but when it is 2 
or more, it still shows the price of one.

I'm using 4.8.7.

Flypage (SalePrice is a custom field):
[discount [item-code]] $s + [item-field SalePrice] - $s [/discount]

Cart is using:
[if discount [item-code]]
and within that:

[discount-price] for the price of one (works correctly)
and
[item-discount-subtotal] for the extended price.

I noticed the tag [item-discount_subtotal] in the docs, but I guess the 
hyphen is an alias for the underscore, as it didn't work either when I 
tried it.

Is this tag not working properly, or am I missing something here?

Thanks,
Josh