On the start page each time you hover over a game a grey outline appears around the edge, assuming the new start menu is done using the same tools as developers I presume the issue is stemming from UIStrokes as this only occurs with the new UIStroke beta.
What I presume is happening is each time you hover over a game a new UIStroke is added to the frame.
Expected behavior
The highlight/outline to stay the same brightness each time you hover over it again.