Robert Oster Chicago ink flow got wetter, darker the next day

This is strange.

Somehow the ink flow in the same pen got wetter a several hours later, towards the end of the same converter fill, resulting in darker and less green-leaning ink marks even on the same sheet of paper. The pen was cleaned and dried weeks ago, and so it would (or should) not be a case of remnants of moisture in the feed diluting the ink while I was writing the body of the ink review.