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When adding elements using dg.add() method, if you add some rows it should enable the scroolbar when there are some rows hidden. That's not what is happening.
You need to use the mouse wheel to scroll down or up in the datagrid widget so the widget realize that it needs to enable the scroolbar.
How to reproduce:
create a datagrid setting its height to 100px and add 5 element rows using .add() method.
PS.: this bug is true for dg.remove() too. When it should recalculate the scroolbar height and hide it if necessary, it simply removes the row but the scroolbar thinks that there are the same amount of rows as before.