I too, witnessed this behavior with the Phoenicians after having researched Calendar.

Hello!

We have a known issue that causes the Power Investor to not work  when used just after unlocking the technology to exploit a Luxury or Strategic resource deposit. While we're investigating a solution, save and reloading the save after unlocking the technology should work as a workaround.

Trully sorry for the inconvenience.

This still appears to be an issue. Your workaround to Save & Reload did work. If you guys are bored over there, I would venture to guess that the requirement check to determine if Calendar has been researched occurs during the start of one's turn. However, there is a decent chance that you can pick up Science through curiosities in the Ancient Era which may complete your research mid-turn and missing the check. Or it could be something else completely, just what it seemed like to me. Cheers. 

Bump! It is still there, loading the save works as workaround.