You have chosen a combination of Bar Styles and Text Styles that makes some of your calendar bars different heights. As a ...

{You have chosen a combination of Bar Styles and Text Styles that makes some of your calendar bars different heights.  As a result, you may want to position these bars independently of the snap-to grid in the view.

You can hold down the CTRL key while moving tasks in the Calendar view to override this grid and place tasks anywhere in the view.}