The following bug appears at first random. Much depends on screen size, as it gets smaller the bug is more prominent covering more or less buttons. The placement of the left and right popup menus while not-clicked or not-visible interfere with actually touching the main timeline buttons on the menu bar. My fix was to increase the z-index of the main menu bar to a very high number but this is a css work around. Others may just think the buttons don't work. The example images below I have taken emulating a phone screen at 400px by 650px. Thank you for the wonderful new timeline feature.
Varies by device and screen size.
Damn it the other bug report made it in.
This annoying little bug should now be gone. It fought bravely but was ultimately bested.
Haha well said. It took me a bit of tinkering to isolate and figure it out to report. I removed my z-index and can confirm my buttons function.