Not Charging On USB Connection

[Spey]

Device is not charging on USB connection.
I remember seeing this control to turn on/off this option, but can't seem to find it now.
Previously charged on this USB socket (when idle, screen on/off, and when controlling device from computer).
I remember this setting being directly tied to charge with screen on and/or off, etc.).

Hope someone could post where this setting is?

[Spey]

Well, I found a work-around (not the solution I was looking for, so please post up alternate solutions!).

It appears the device (Razr M running OTA JB at least) will not charge on USB when "USB computer connection" set to MTP (will charge on USB on PTP).
Where to find/how to change ...
When device connected to computer via USB the two Drop Curtain options as follows:
Connected as a media device (MTP) >USB Charging does not work
Connect as Camera (PTP) >USB Charging works

Anyone's explanation for why this would be would be appreciated.