It's not about disconnecting from the external display (the OSK won't be shown then if a BT keyboard is present), but rather picking the device up and using its virtual touch pad feature.
Conversely, bug #1521518 discusses the opposite being a problem on the main screen - that there is no way to invoke the OSK when an external keyboard is connected. ** Also affects: ubuntu-ux Importance: Undecided Status: New -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1580143 Title: OSK appears when device is connected externally over HMDI with BT conected keyboard To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-ux/+bug/1580143/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs