The two dates are the same, just the string representation is different. For instance, these are all the same exact time:
new Date('Mon Apr 28 2014 15:00:00 GMT+0100 (BST)');
new Date('Mon Apr 28 07:00:00 PDT 2014');
new Date('2014-04-28T14:00:00+00:00');
new Date('Mon Apr 28 2014 10:00:00 GMT-0400 (EDT)');
So any calculations and displays should come out correctly. Now, why you are seeing a different timezone seems strange since, AFAIK, every browser simply uses your system clock.
However, you've commented that you're using a virtual machine to test IE. It is quite likely that that VM has a different timezone set and that's why you are seeing a different text representation in IE.