The root will grow for a long way underground. The visible leaves can pop up anywhere along the root. What I have pop up in the yard now is usually from a root I missed.
Brush-b-gone does work better for the big stuff (root etc), you can just paint it on the root where cut and it really works great.
I need to post some pics tomorrow of some tremendous poison ivy growth at my place of employment. Looks like branches of the tree, but its not.
Unbeknownst to most, and only recently beknownst to me, is the fact that MANGO is in the same family as poison oak, poison ivy and poison sumac, and its sap and leaves (not the juice inside the fruit) contains the same "active ingredient." Two weeks of a nasty rash around my mouth, chin and the tip of my nose taught me that lesson the hard way. Be forewarned!