edit other field that date field change the date field value ( only second)

-- HikaShop version -- : 2.6.4
-- Joomla version -- : 3.6.2
-- PHP version -- : 5.5

Hi
I use unix timestamp storage default date field ( product_sale_start product_sale_end).
When i edit a product that mean i change the value of a field that is not product_sale_start then when i click on save button then the second value of this field change. Since i try filter on that field then my result is random and nothing work !!

Could you please fix that bug that when edit a product without change manually by keyboard the field date that the value second attach to that field don't change . the year mont day value stay to the same value only second change !!! The second can't be edit using the date picker only manually but here i don't change the date value anymore nor by hand/keyborad or by date picker !!

How joomla could be stable if date is store in unix format and second is define by random !!
Why hikashop in joomla 3 dont use joomla date picker that support more ( hour minute ) than the hikashop picker
I m not a core developper but why the second are random beetween the web page form and the rdbms unix timestamp ?

I test on joomla article and edit other field than date don't change the second value in the article edit page mode !!

for give some information of how date change in the rdbms .
1498593600 after save become 1498590000

You don'think my capture screen are not real or is fake !! The capture screen come from my webserver with joomla 3.6.2 and hikashop 2.6.4 . what i see is that date picker in joomla manage minute second and not the date picker that appear when edit hikashop product .. it is the reality nothing virtual ....