Angularjs IE9 refresh strange behavior

Angularjs IE9 refresh strange behavior

I found this issue when learning Angularjs's scope example. Here's my code:
<span data-ng-controller="Control1">
<input id="a" data-ng-model="model1.input1">
<input id="b" data-ng-model="model1.input1">
The input is: <span id="c">{{model1.input1}}</span>
The input is: <span id="d">{{model1.input1}}</span>
</span>
I can see it works, just the synzhronizing behavior is strange. When I
start to type in either , both content are synchronized, but the view part
{{model1.input1}} doesn't synchronize, sometimes only one
{{model1.input1}} is synchronize. But if I double click the page, or
select all text in the input box, both {{model1.input1}} are synchronized.
My browser is IE9, it works perfectly on firefox and chrome. Anyone have
idea what's happening? Thanks.