This warning message, to Stay or Leave a page, shows up only when an entry has been made and you are trying to navigate away from the page without saving the entry. The issue You are noticing seems to be browser related, because the message is showing up when viewing receipts in Expenses. Have you noticed the issue on any other browser apart from Internet Explorer? If the issue is not repeated on any other browser, try clearing cache and cookies, restart Internet Explorer and check.
If the issue persists please contact Replicon Support