I just noticed that the scrollbar only follows the content of the EditText. If you start dragging the scrollbar, the content will intercept the touch and will scroll on the opposite direction of the scrollbar:
It works different in a ListView, where you can actually drag the scrollbar and scroll the content.
Another user pointed out this issue here, but I don't think he got the response he needed.
Anyone found a solution to this problem?
In case it's needed, this is the code for the example:
<EditText
style="@style/customScrollbar"
android:layout_width="200dp"
android:layout_height="200dp"
android:gravity="top"
android:inputType="textMultiLine"
android:scrollbarAlwaysDrawVerticalTrack="true"
android:scrollbarStyle="outsideOverlay"
/>