Setting Time.timeScale to 0 on a button press, will freeze that button in the Hovered state, and will make that button "selected", so you can't press any other button while timeScale remains set to 0.
To reproduce:
1. Create a new Scene and add a new 2D UI,
2. Add 2 buttons to the panel: Button1 and Button2
3. Add a script that simply sets Time.timeScale=0; as the "OnClick" target for Button1
4. Add a script that prints "Hello" to console as the "OnClick" target for Button2
5. Run the game, click Button1 to "stop" the time.
6. If you try to click Button2 now, you'll see that it doesn't respond, but instead Button1 is being clicked.