md-input-container with md-prefix produces unexpected DOM

[parker-mike]

Bug,
<md-input-container> <span md-prefix> <md-icon>home</md-icon> </span> <input mdInput name="givenName" readonly disabled> </md-input-container>
gives wrong DOM, div.mat-input-prefix is empty while the span.md-prefix is generated inside div.mat-input-infix
could be seen on the following plnkr:
http://plnkr.co/edit/WRtJEaWx0ilHPBeGLSM5?p=preview
which is regression from beta.6 on 4.1.3:
http://plnkr.co/edit/dGxYTBaObsjDs557jM4k?p=preview

[willshowell]

mdPrefix works instead of md-prefix though I don't totally understand it

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