That's why it is dependent on the time of the device at the time of "conception".
And was this back when they were first added to the game? The theory is either that the game went gonzo before Christmas and the servers couldn't handle all the new sign ups resulting in glitches OR the rules for breeding Suns and Moons have changed.
I have been given access to a test account with unlimited gems for speeding up the breeding process. I have run 500 "copulations" in the last few days, resulting in 28 Sun/Moons. All Suns were created between 7am and 7pm. All Moons were created between 7pm and 7am. Save for one series I did at 1:15pm, where I changed the time on my iPhone to 2:15am. I created 2 moons in a group of 50 pairings.
Now my sample is quite small, but the results are pretty cut and dry. In one group of 50 pairings of Cold + Firefly I created 6 Suns and 0 Moons. The other members of the forum that are running tests at
New look to the breeding process are having the same results.