CSS Styling "Lost Intermittently" on Mobile

Hello. I’m not certain where this post may belong, but I thought I’d try WordPress first hoping someone may have seen it before or can identify the issue. I have a created a semi-responsive design for a site at: http://staffordhills.com/wordpress/ The desktop version works exactly as I’d like. But there is a mobile CSS for “@media all and (max-width: 480px)”. Generally, this works exactly as I’d like too… UNTIL… browsing around a bit on a Samsung Galaxy S2 in portrait orientation, for example, the CSS styling suddenly seems to drop. I can’t get it back until I clear the mobile browser cache and refresh. I can’t identify why it occurs or even if there is a pattern. It really seems random to me. I can lose CSS after 2 clicks in the main navigation menu or 50 clicks. The research I did seemed to possibly point to AJAX/Javascript issue involving refreshing and the creation of a list view or something like that. Since I did not place any Javascript in my theme design (and am not a programmer), I turned to my plugins as possible culprits. I use two that I suppose could be suspect: jQuery Colorbox and Riva Slider Pro. I disabled Riva Slider Pro first and was able to duplicate the issue. So I additionally disabled jQuery Colorbox. Truthfully, I haven’t been able to duplicate the issue since I disable the jQuery Colorbox, so I am thinking that MAY be the issue. But I’d like to know FOR SURE so I know that the issue is resolved and I’d like to understand the issue a little more. Can anyone out there shed any light on what I’m facing and/or duplicate the issue?

Oh, and I should mention that the plugins are both active again at the provided address.

Thanks!!