Incorrect Variant Being Added to Cart

[PSGadmin]

Currently I have some customers that when they add product of the 100 count or the 1000 case count the item in the cart ends up being the lowest value of a 10 pack which is the default value on the product page.  I try to replicate the error and cannot figure out how they are getting it to happen.  It does not happen all the time but for some customers they can not get out of it.  I have removed the item from the cart before and then added it back and that seemed to work but it doesn't work for some customers.  Any help in getting this fixed would be appreciated thanks!

[PSGadmin]

I forgot to add that the website is www.prosupplyglobal.com.