[3.0.1] DatePicker doesn't "un-grey" dates when browsing through months

[jtaekema]

August 22, the date picker is first opened the dates are grey'd as appropriate.
date-chooser1.png

Choose September.
The date picker will grey Wednesday through Friday on the first row as expected. However, Saturday 29th and Sunday 30th are still grey from the previous month, it doesn't "un-grey".
date-chooser2.png

Go back to August, Wednesday 1st through Friday 3rd are still grey, when they should be black.
date-chooser3.png


Browsing through more months will cause more dates to become grey but they never become black again.

[jtaekema]

It is worth noting that this bug is visible in the examples.

http://www.sencha.com/examples/#ExamplePlace:datepicker