There's a bug in IE10 that makes setImmediate and MessageChannel practically useless on IE10 Mobile, and somewhat unreliable on IE10 Desktop. Simply adding a spin.js spinner on our login page caused Q promises to stop working on IE10 Mobile.

I wrote a detailed description of the bug in my blog: http://codeforhire.com/2013/09/21/setimmediate-and-messagechannel-broken-on-internet-explorer-10/

As a workaround, we had to disable both setImmediate and MessageChannel in order to get Q promises to work:
window.setImmediate = undefined;
window.MessageChannel = undefined;

when.js seems to use setImmediate if present, so it's affected as well. See kriskowal/q#396