Steps to repro:
1) Run this test: https://drive.google.com/file/d/0B-p_FKXYznm5cGJJbUlab09hYlE/edit?usp=sharing
Expected: when you use the AjaxTimeout property on step 2) - it will wait for the dropdown list to be populated by an AJAX request before moving to the next step and the test runs successfully.
Actually: step 2) doesn't wait for the AJAX request. As a result step 4 fails with Index was out of range. Must be non-negative and less than the size of the collection.