Nexus 5 sold with Key Lime Pie test build on board
The phone's boot-up animation was similar to what was used for Ice Cream Sandwich (Android 4.0) and the codename Hammerhead can even be found on the Settings page. When a phone is bought with an old OS build onboard, it usually is quickly updated to the current build once the phone is activated. But with this phone containing a test version of Key Lime Pie, it is not eligible to receive OTA updates. As a result, the buyer had to have Android 4.4 flashed onto his device.
While this was nothing more than a small little bump in the road on that highway we call life, at least the buyer of the phone has a wonderful story that he can tell his kids and grandkids for years to come.
source: XDA via AndroidandMe