Basically the same bug as MCPE-230832. The mouse cursor is no longer bound to the window and can interact with other open windows.
Steps to Reproduce (video pending):
Have a second window open while playing Minecraft. A picture-in-picture YouTube video works best.
Move your cursor the wrong way.
You will be able to pause the video without meaning to.
As mentioned in my comment on MCPE-230832, please include steps to reproduce the issue and a video.