Drawer: mdl-layout__drawer, aria-hidden is always "true"

MDL version: 1.1.3
Browser: Chrome
Browser version: Latest
Operating system: OSX
Operating system version: Latest

What steps will reproduce the problem:
1. Code a MDL layout with fixed drawer

``` html

```

What is the expected result?
.mdl-layout__drawer `aria-hidden` attribute should have value "false" when drawer is visible

What happens instead of that?
`aria-hidden` attribute is always "true"

Please provide any other information below, and attach a screenshot if possible.
Inspect drawer element in any browser