The ion-tab directive currently does not support the binding of scope variables to it's attributes.
For instance to set the title from a scope variable tabTitle one can do
<ion-tab title="{{tabTitle}}" ...
but not
<ion-tab title="tabTitle" ...
This means the tab title will always be set to a fixed value and any later changes of tabTitle will not update the title attribute of the tab.
As far as I can tell this is true for all attributes of the ion-tab directive.