Charing problem w/APC UPSes

[lindend]

My Nexus 4 charges at full power when plugged directly into a wall, A/C adapter in a car or to a power strip in a wall. However, it is quite erratic when plugged into APC UPSes (tried several of them). Most of the time, it indicates that its charging at USB strength and not A/C although sometimes if a unplug/replug it in enough times, it will show A/C charging. Worse still, a decent percentage of the time, it gets in this rapid charging/not charging or AC/USB charging mode which actually drains the battery. I've ruled out the power cord/adapter and it definitely only happens when connected to the UPS (both the battery backup side and non-backup side). Anyone else experienced a problem like this?