Just noticed in recent versions of the notebook that there is the text "Run" in the run button in the notebook toolbar. No other buttons have text:

What the motivation behind this? It is pretty non-standard in a UI like this to put text in a toolbar button, and the "play" icon here is one of the most universal icons. Here is Google Drive and Word:

We would need a really strong reason to add something like this - such as strong evidence from well run multi-person usability study. We would also need to understand if out choice of the "play-stop" variant was the problem and that another icon wouldn't solve the issue. Outside of evidence like that I think we should revert that change before the 5.2 release.

@gnestor