Ok than clearly the search has to continue in Kodi.
The fact that it might be impacted by the switch from 16 to 17 could indicate a topic how input devices are treated
Does that mean only Team Kodi can issue a fix for this?
I doubt they will be interested. 
Well yes and no. Generally if you can replicate the issue also on libreelec than your best bet would be the Kodi Forum. But you may want to first provide debug logs here maybe someone has an idea. But as your problem is different to this thread (yours is working in the console) you should open a new thread.
The plot thickens…
I got my Vero 4K and the numbers work fine. Yay! So the issue that exists on the Pi3, doesn’t exist on the Vero 4K.
But…
Something interesting I have also noted when adding a source name. If I click the box and bring up the virtual keyboard, text entry is fine, but I can’t move back and forward through the name because the arrows just move the highlight around the virtual keyboard. OK, that’s expected behaviour so it’s fine with me. However, if I exit the virtual keyboard and just use the cursor in the text entry box with my keyboard, the space bar doesn’t work. 
I am going to try disabling the virtual keyboard in settings to see if that changes the behaviour.
EDIT 1: Disabling the virtual keyboard makes things worse. Using the cursor the space bar still doesn’t work. Hitting enter to modify the text is the same as with the virtual keyboard, only now the directional buttons do nothing.
EDIT 2: Confirmed the same results with standard keyboard.
EDIT 3: Sorry. I know this has gone beyond the original title and it needs a new thread, but since the history was here it was easier to just update it. Hope that isn’t annoying anyone.
Do you have another keyboard at hand, even wired, to quickly test with?
Sam
Yes Sam, see my 2nd edit. I tried with a wired keyboard and get the same result. 
IIRC, spacebar only works as a spacebar in the virtual keyboard dialogue. Otherwise it is intercepted and used to pause/start any media playing.
In the keyboard dialogue, arrow keys work to move the typing cursor when the focus is on the text entry box.
Does that fit your symptoms?
IIRC, spacebar only works as a spacebar in the virtual keyboard dialogue. Otherwise it is intercepted and used to pause/start any media playing.
Possibly. But surely it would make sense to have it act as a space bar when in a text entry box? i.e. before clicking to bring up the virtual keyboard.
In the keyboard dialogue, arrow keys work to move the typing cursor when the focus is on the text entry box.
While in the virtual keyboard dialogue, I cannot put the text entry box into focus, only buttons on the virtual keyboard. 
I did find that I can use the arrow keys to move around the focused text entry box (before clicking to bring up the virtual keyboard), if I hold down the control key.
Ideally I would like to ditch the virtual keyboard because with a mini keyboard it is totally redundant.
Are you aware of the Chorus 2 browser interface?
You can then use your laptop/PC keyboard for text entry, as well as generally controlling Kodi.
I just tested this myself. Everything is working as expected. At the start whie you can type in the text box with your keyboard the “focus/cursor” is on the “done/cancel” dialog so that when you press enter it automatically is executed. That means when you use the cursor (left/right) in that moment you only will change between Done/Cancel to move in your text you need to press cursor up once then left/right moves in your typed text.