This is related to
OFBIZ-278. This reminded me of it and I think I've found a solution for OFBIZ-278 that would take care of this as well. I'm going to test my guess and report back later today.
Looking over your patch, why do the screen.render at all? Why not put
<if-compare field="inventoryItem.inventoryItemTypeId" value="NON_SERIAL_INV_ITEM"/>
<include-form name="ViewPhysicalInventoryAndVariance" location="component://product/webapp/facility/inventory/InventoryForms.xml"/>
<include-form name="CreatePhysicalInventoryAndVariance" location="component://product/webapp/facility/inventory/InventoryForms.xml"/>
and remove the final conditional test from the end of EditInventoryItem.ftl