Yea...it did not lose prime very often but as was previously stated, it never happens on a warm sunny day....And "Yes" Meaux you are correct about turning on the water when the electricity was out.
And that can happen very easily. How many times have you walked through your home when the electricity is out and walk into a room and flip the light switch....

...It's just a habit. Same with turning the faucet on. As a kid, I always blamed my brother....