Electron Battery charging - via USB and VIN

What am I missing here:

A. Using the USB connect, the battery charges AOK - red led comes on, stays on for a time, goes out.
B. Using a 5V source through VIN, battery does not charge - red led come on and stays on forever.
C. Using the same 5V sources through the USB connector, the battery charges AOK - red led comes on, stays on for a time, goes out. {yes, I cut up a USB cable to make this happen}

From the block diagram, it appear the 5V from the USB connector and VIN are connected together and then connected to the power management subsystem.

Suggestions?