You can observe the behavior in this link. When you click on the button "Comment" it opens the modal, shows the header / title and then scroll down inside the modal.
<md-dialog-actions layout="row">
<md-button class="md-raised md-primary" ng-click="cancel()">Cancel</md-button>
</md-dialog-actions>
I think it is the md-dialog-actions tag, because when I comment it, the modal doesn't scrolls down, but I have no idea how to fix it.
In your controller you should include the "focuOnOpen: false" in your showDialog function, just like the following:
showDialogDonation() {
this.dialog = this.$mdDialog.show({
focusOnOpen: false,
});
}