I wrote a very simple test sketch and the EEPROM values are working for me. Value is saved across removing power. Photon, 0.4.9 system firmware. You’ll probably have to provide more info (hardware, software versions, your code).
The Eeprom code has had a major overhaul for the upcoming 0.5.0 release which addresses a number of corner cases where the eeprom could be corrupted during power failure.
The 0.5.0 release will be made available as a pre-release soon - I hope you’ll be able to help us test the new eeprom implementation.