Sub-Menus Disappear When Window is Resized from Mobile to Full

I’ve found that when I resize my window from a size that’s small enough to trigger the mobile menu, to a size large enough that the full menu appears, no sub-menus appear when I hover over the appropriate primary navigation item. (You can see the problem on my site with the “About” menu – Please ignore the fact that none of the links actually work; I’ve changed them all in preparation to move my site from the /wp/ subfolder to the root.) I can see this being a problem for anyone who starts by viewing my web site in a smaller window, then maximizes it; they will not have access to any of the pages linked from the sub-menu.

To give credit where credit is due, this is really the only thing that’s keeping me from giving Sydney a 5-star review; I’m a big fan of it in all other respects, including responsive/mobile design, but I’m not looking forward to completely redesigning the menu options.

I have the same problem on my Sydney theme. After I updated it to last version several problems happened. This is one of the main problems, but also the white line above main slider is showing up when page is opened in mobile size, and than resized to full screen size.
My site is
The problems are also showing up at athemes demo site of Sydney.
Any news about solving this problems?

Please help. I think these are some nasty bugs.