When duplicant get skill increase the tooltip show wrong number. Sometimes tooltip guess it right, but most of the time number is wrong. Both ways.
Ceterum censeo bugs involving loss of resources mass like pumps, plumbing, water going downhill by steps, airlock doors in a row and so on should be attended with priority as affecting fundamental aspects of the game.
Wait for skill increase -> Pause -> Check tooltip info -> Compare it with stats pane.