Selenium does not see a screen is present - introduced after Windows update - selenium

Question

I have a fairly large set of Selenium tests (about 180), which have worked very well over a long period on XP and Win7 32/64bit machines.
Recently, after a Windows 7 update (which may be coincidental), the tests have become unreliable. They fail at random, but always with the same problem - an expected screen is displayed but the WaitForPageToLoad() method does not return to confirm this. This does not occur on the XP machines, only the recently updated Win7 machines.
Platform: Win7, 32 and 64bit, Selenium 1.0 and 2.33.0 (no difference in behaviour), VS2008, browser IE9.
Scenario: A test initially displays a 'restart' screen with a single button, clicks on the button which should launch a login screen (all the tests go through the same code to do this). The login screen is displayed in the browser but the test line
selenium.WaitForScreenToDisplay(30000);
does not return so the test times out with an error message. The tests will fail in this way completely at random - about half of them fail, but not consistently the same ones.
The application itself behaves perfectly when a human being interacts with the browser. The selenium logs don't give much in the way of clues - the last line is always 'waiting for page', eg "....Command request: waitForPageToLoad[30000,... ]".
Stepping through the test in the VS debugger never reproduces the problem.
The actual code where the problem manifests itself is
selenium.Open(GetRestartPageURL());
selenium.WaitForPageToLoad("30000");
selenium.Click("Button");
selenium.WaitForPageToLoad("30000"); <-- this is where it times out even though the expected screen that is launched by "Button" is now displayed in the browser
Is there a known problem, or a workaround for this? Is it an issue with IE9 and Selenium 1.0? Its come out of the blue at a critical time.

Answer 1

This turned out to be a bug in IE9/10 and/or selenium, or at least a bug in IE9/10 that the selenium folks do not look like addressing any time soon. I worked around it by writing my own WaitForPage method that looks at window.document.readyState in the browser and also monitors the delay so I still have a timeout.
Here's the code, if it will help anyone else:
internal static void WaitForPageToLoad(ISelenium selenium)
{
//Wait until the browser reports that it is no longer loading the page, or 'timeOut' has been reached.
//Pause 1/4 second between attempts (should normally be sufficient for the page to load, unless it is a very slow page)
const int timeOut = 30000; //mS
const int pause = 250; //mS
int timeWaited = 0;
do
{
System.Threading.Thread.Sleep(pause);
timeWaited += pause;
}
while (selenium.GetEval("window.document.readyState") != "complete" && timeWaited<timeOut);
if (timeWaited >= timeOut)
{
//abort test and notify error:
Assert.Fail("Expected page was not dislpayed");
}
}
There are two issues in the Selenium bug tracker referencing this bug: 1639 and 2451