The best tool to break pumpkins or melons is an axe, but the ring of correction does not switch to the axe when breaking them. The ring of correction does not switch to anything specific either, just remains on whatever tool you have in hand.

The axe is the quickest for both pumpkins and melons, as seen in the minecraft wiki:

• http://minecraft.gamepedia.com/Melon_%28block%29
• http://minecraft.gamepedia.com/Pumpkin

This is another very easy fix. Material.gourd just needs to be added to the materialsAxe array in common/item/equipment/ToolCommons.java.

I'm not sure if a single line fix is worth a pull request, but someone with write permission can fix this quite easily.