From reddit:

When right-clicking with a pickaxe, if I have a torch on my hotbar, a torch will be placed. Since I'm mining with a dowsing rod in my offhand (or I guess trying to), this isn't exactly helpful.

Does anyone know which mod adds this functionality and how to turn it off? I've looked through configs for Inventory Tweaks and Mouse Tweaks and found no such setting, and have no idea what other mod could it be.