When in World Selection (Singleplayer), the 'play' icon for selecting the world appears to be incorrectly shifting position.

If you attempt to open a world saved in a newer version of minecraft, than the version you're running, it will warn you and show you the exclamation mark – this is intended behaviour because there will likely be incompatibility issues.

However, if you attempt to open a world saved in an older version of minecraft, than the version you're running, the icon should stay central but it's now shifting to the right.

I've tested this on 1.11, 1.12 and 1.13 with expected results. The icon only appears to shift as of 1.13.1. (Using Default texture pack only).

Screenshot – -969535336 1.13
I'm running 1.13.1 and hover over a 1.12.2 world and the icon moves to the right.

Sreenshot – SquidBrush 1.9 1.10
I'm running 1.12.1 and hover over a 1.9.4 world and the icon stays central.