I'm in 17.10. Whenever I touch the screen, whether to change windows/apps, scroll within a browser, or press a button, the stupid little keyboard pops up in the bottom left corner.
I have never left Screen Keyboard enabled in Universal Access, but if I toggle it on, that's the same keyboard popping up in the bottom left corner.
In this screenshot, I'm simply touching the screen in a full-screen youtube video. You can see the menu pop up on the right, under the point where I'm touching.
I don't have a before pic, but it was similar look/color keyboard, but it was smaller, maybe half as wide, and only in the bottom left section of the screen, as opposed to stretching across the entire width. This change from little left-hand keyboard to full-width keyboard happened after following @pomsky 's advice below.
This is a confirmed bug. You can mark yourself affected by it to hopefully increase its received attention.
Best Answer
Caribou also kept popping up to my great annoyance, so I wrote a gnome extension that monkey patches gnome-shell to stop popping up the keyboard when the touchscreen is pressed.. It's only a couple of lines of js, but the git repo is here
How to use extensions
To manage gnome extensions, download gnome-tweak-tool with
Gnome extensions are downloaded through the official gnome-extensions website, which requires a native connector to communicate with gnome-shell. Install this native connector (even if you're running Firefox) with
Finally to install the extension, go to the extension's page and hit the switch in the top right corner. Gnome will than prompt you to install the extension. These extensions can be managed through the gnome tweak tool. However, to uninstall them, you must use the web page.