Dialog: overlay causes browser scrollbars to appear after window resize

Steps to reproduce:

1. On page with no visible browser scrollbars

2. Open modal dialog

3. Notice no visible browser scrollbars

4. Close modal dialog

5. Resize browser to be smaller

6. Re-open modal dialog

Excepted result: no visible browser scrollbars

Actual result: visible browser scrollbars

Reduced test case:

http://jsbin.com/ebavab