Divine font returns lvl 19 gem

When using the divine font in labyrinth with a lvl 20 gem to "transmute into a random gem of the same colour", the returned gem is quite often returned as a lvl 19 gem

To reproduce:
Take a lvl 20 gem
Toss it into the divine lab at the end of the eternal labyrinth
See if it returns a lvl 19.95 gem