Sort button is not positioned properly when using Iron Chests mod

[campbellcole]

In any chest added by the Iron Chests mod, the sort buttons do not render properly when the container is first opened:

However, if another GUI is displayed and then closed to return to the container, the position of the buttons change to where they're supposed to be (to test this, I opened a recipe from JEI while still in the chest, then pressed escape to re-render the container GUI):