Under setting ther will be "Language & Input" >> Keyboard Setting >> "Input method selector" >> "Always show"
after you plug in the keyboard just put on the Keyboard ICON "on the bottom right of the screen" the select "USE PHYSICAL KEYBOARD" to off
Then the Soft keyboard (on screen) will appear normally until you unplug the keyboard.
In my case i use the barcode scanner instead of keyboard so I do need some softkeyboard however I use the USB hub and connect both barcode scanner and numeric keyboard.
hope this will help you.
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