http://forums.openqa.org/thread.jspa?threadID=10173

SeleneseTestCase.checkForVerificationErrors has a bug. It's code is:
public void checkForVerificationErrors() {
assertEquals("", verificationErrors.toString());
clearVerificationErrors();
}

So, if you look closely, if verificationErrors isn't empty, it will never be cleared, because assertEquals will throw an exception. You should put assertEquals in try block and clearVerificationErrors() in finally block.