Pogo pins power clarification - reading schematics

[dsimic]

My guess about why GregH's phone didn't catch on fire would be that the output of LPW5206 was at exactly 5 V, while the external 5 V source was actually slightly below 5 V.  As a result, the output of LPW5206 was able to "beat" the external source, while the external source had some kind of protection (most probably an isolation diode) that prevented power from feeding into it.

Edit: Even if the external 5 V source was at exactly 5 V or even slightly higher, so the output of LPW5206 was unable to "beat" it, our beloved D600 diode prevented the external source from reaching the LP6226 or PS.  However, all this should be avoided, IMHO.