Reproduction steps
----------------------
1) Open user's project (UI sample project from the asset store)
2) Build and run scene 'Lighting' on a device
--- Only one light is affecting the UI 'Dynamic UI Light'
--- 'Extra Light' which should bask the lower right corner of the UI in blue glow is not present

Another strange thing in this scene:
3) Reduce 'Green' slider to 0%
--- 'Dynamic UI Light' will switch off and the 'Extra Light' will turn on

Reproduced on:
Android
iOS (GLES & Metal)

No repro:
Editor
OSX Standalone
Windows Phone