So, after discovering that upgrading a tool caused you to lose mining and farming experience, I focused primarily on upgrading my armor.
My armor was at level 109. My tool was level 1. The tool had about 100 durability left, so I refreshed it using a talent.
After this, the tool suddenly shot up to level 109 to match the armor I was wearing. This, of course, caused the tool to change, and the experience gained from mining and farming were once more halted.