[TYPO3-shop] Problem with user % discount field

[RF]

Hi,

I've this problem with tt_products.

When I set a number < 10 for the discount % in the user's form and I 
"save" ... the number became 10.

Is It possible to set discount less then 10? ...I've to set 5% of 
discount for an user.

Is it possible to set a discount for all user under a group?

For example: 5% of discount for all user under "user group"=2.

Thanks,
Roberto