You may have ran into this issue when trying to bind a submit button with multiple disable conditions. The easiest way to do this is to embed the variable checking in the html as follows:

Both variable must be false for the button to be disabled:

<button class="button" ng-disabled="(!data.var1 && !data.var2) ? false : true">
</button>

Either variable can be false for the button to be disabled:

<button class="button" ng-disabled="(!data.var1 || !data.var2) ? false : true">
</button>