I am having the same exact problem described here:
The JS fix offered in that post doesn’t fix the problem for me.
Create an ASP.NET default application, 7 links (which I have), and it doesn’t collapse when it’s supposed to. Instead, the nav becomes 2-3 lines and blocks page content that lives under it. Shrink the browser some more and then ir properly collapses.
Any advice for a fix? It shows up by default this way on the iPad (nav spreading over 2 lines) and I cannot resize the window to make it collapse and show the missing page content.