Vaadin 6 app embedded in frame behaves odd in IE10

I have a small Vaadin 6 Application (6.8.9) embedded in frame, being a part of larger legacy web app created with JSF1.x. Main app has several frames inside main page:

  1. Top - just displaying logo
  2. Left - navigation bar
  3. Right - content (this is the frame V6 app is embedded to)
  4. Bottom - just a logo.

Nav bar is implemented in JS, all it does is set content frame url as below:

top.context.location.href = ; // context is the frame name

Main page has the following HTTP header:

Problem is reproducible
in IE10 only
: when user clicks on link which points to V6 application, it is displayed with no issues. Then user click on any other link in nav bar - frame is grayed out, mouse pointer turns to vertical resize icon (why???) and nothing happens. If user then clicks on frame content, it seems to re-load and displays correctly.

Any clues on why this happens? What this gray screen with odd mouse pointer means? How to overcome this? Or can anyone suggest on how to debug this further?