This has been occurring for as long as I can remember - with previous versions also.
If I select some text to change it’s font the adjacent next character that is not selected changes to the new font.
As you can see – once selected, the space after the character 4 also gets selected even though I have specifically placed the caret directly after the 4.
This only seems to happen when selected with the mouse – if I select with the arrow keys, the space after the 4 does not get selected and the next character’s font does not change.