My streambar turns on my TV when I press Home. Do you have "1-touch play" enabled/checked under Settings->System->Control other devices? Is it connected to the same TV that the Ultra was connected to? If not, does the TV support CEC?
My Streambar will return to the Home Screen whenever I turn off the TV, so if you're pausing a video and turning off the TV, that's probably what's happening. I think connecting the Streambar through a powered HDMI switch might keep this from happening (from an old discussion), but I don't know if there's ARC issues when using a switch.
As for launching (or installing) various channels, are you using one of the screensavers that has little advertisements floating by? If so, don't press Play on your remote to dismiss the screensaver or it will activate the ad.
Don't wait for Roku to "fix" anything (which first assumes you can convince them that something's broken). My philosophy has always been that you find workarounds for Roku's many limitations or use something else (or just keep banging your head against a wall until you can't remember what you were frustrated about). Not to mention, they never respond to such questions other than to say keep an eye on their blog.