It seems the interaction does not work the way you would expect. I have not taken screenshots unfortunately, but playing secrets like explosive trap after playing celestial shot will not do the expected 4 damage but the normal 2.
It works exactly as expected. Secrets need the spell power effect active at the time they trigger, not when they’re cast.
Celestial Shot only applies to the spell cast after it, then the effect is consumed. So casting the secret consumes effects like Celestial Shot, so they can’t be active when they’re needed.
It’s the equivalent of having a spell casting minion on the field, casting a secret, having the minion die, then expecting the secret to still have the spell damage bonus. It doesn’t work this way. This isn’t a bug.
I mean, the guy posted a bug report, so clearly he didn’t expect it…