This is a known issue with single-field forms in IE. Pressing the enter key does not call the "first-next" button of the form, and therefore its name = value pair will not be displayed on the query parameters map, and therefore, JSF will not be able to identify the button to queue the action event.
One way to fix this is to add a second, but invisible input field to the same form.
<input type="text" name="dummy" style="display: none;" />
This will cause IE to also send a name = value pair to the first-next button.
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