1 custom field value disseppear using dropdown

-- HikaShop version -- : 2.3.4
-- Joomla version -- : 2.5.8
-- PHP version -- : 5.5.8

Hi
I create a custom filed for product name. I test how filter work by take care of items in the seach box and result in the main area page .

a) When i switch from checkbox to single dropdown in BE , in the FE one item disseppear !!
It seem the value that appear in the filter search must be enter manually during configuration of the filter even if the the values have already be define manually for this custom fields value during the creation of this custom field !!

b) I don't understand the documentation about size and number of column . No information is give about unit unit in pixel or unit of cell ( span ?) of the grid layout ? column of what ?

c) why when switch from checkbox to Single dropdown , a new item call size appear ?
size of what ?

Thank's for any informations .

hi
The field for enter item begin to 1 not 0 . This was the issue !!!
it sshould be more simple to manage the item value by hikashop than let end user enter it manually? I think there is a an explanation for let user entre index and value but don't find one ....

regard's