Thanks Emmanuel - yes, those lamps apparently belong to the base plan, which I forgot I had locked. Phew...

After working for weeks on my new home I moved a fluorescent lamp temporarily to get a better view.
Now I cannot move it back, I cannot even select it.
When I use "Select all", all furniture except two of those fluorescent lamps is selected.
How do I fix this - it is all worthless with a lamp ...