Edit Address PopUp Bizarre behavior

-- HikaShop version -- : 2
-- Joomla version -- : 3.3.6

When clicking in the "New" button inside the Addresses Maanger form a Hikashop User menu panel I get this strange result:

The modal windos is at left of the windows, just half to be seen.
The whole browser window gets darkened including the model window and nothing can be edited.
I just can get back to main browser area but nothing editable.

I use a Yootheme template but everything else in the site works perfectly.

I've seen several posts about problems with the addresses modal window but none gave me a clue about my problem.