I do not know if this is really a bug but it’s something that should not happen, basically what happens is that the http://prntscr.com/lzif8n (print) timeline adds up to give play a preview of the vocals.
Although I couldn’t replicate the issue on my devices, this bug has been marked confirmed due to multiple reports of incidents.
I’m mostly sure about the cause though. For more speedy response and fluid experience, in the current release the playhead’s refresh rate has been set to 60 Hz which might be too fast for the graphics to render (or it coincides with your monitor’s update rate). Guess we’ll add an option to slow it down.