We have an App that has a custom tab that is configured to be its default landing tab. Prior to Winter 16, when a user logged in, the custom tab was loaded as expected. Post Winter 16, Salesforce now displays this page:

You will be redirected to https://c.cs23.visual.force.com/apex/TaskList?sfdc.tabName=01r70000000Mb7O.

Click the button below to go to that page.

And the user has to click OK before the expected landing page will load.

This change in behavior seems to be directly related to the upgrade of the sandbox to Winter 16. Has anybody else seen this? How can we fix this?