Wallpress mobile menu issue (floats across the screen)

Hi,
At the beginning thanks for great work and awesome themes. I’m starting my adventure with WordPress and I decided to use your Wallpress theme because it look’s like technologically advanced masterpiece and I want to learn from this :).

But…
I have a Problem which I can not resolve myself, even don’t know where to start.
It consists in the fact, that the menu in mobile version (spartphones, tablets) moves across the screen (or even disappears completly) as you scroll through the page, instead stick itself at the top. This applies to all browsers except Chrome.
devices:

1. iOS (7.0.4) – no problem

• ipad – no problems at all (Chrome, Safari, Delphin)
• iphone (don’t have it, can’t check)

1. Android (4.0.4, 4.1.2) – problem

• 7″ tablet – menu problem on every browser except Chrome
• 4″ i 5″ smartphones – same as above

Desktop version works flawlessly.

 
I don’t know if it is css, php or jquery fault… or maybe some kind of Android “build-in” problem, but if You could spare some time to help me, I will be gratefull.
This problem occurs even after deactivating all kind of plugins and widgets on Your clean Wallpress theme.
I don’t see any errors in CSS code (position is set properly), maybe it is something to do in jquery.custom.js code but I don’t have apropriate knowledge to find check this out.
Please look at this site on your mobile browser:
http://news.architekturaibiznes.com.pl/
 
(sorry for my poor English)