It works ... finally, but I am not entirely certain about the
dependencies.

I tried a new project (and also the one from Helen). Editing the
column doesn't work unless RequestLive is set to true. Editing the
field in IB_SQL when opening the SQL editor from within the
connection doesn't work (I guess the [nameless] query has request
live set to false).

I tried in my real project - it had RequestLive set to true, but no
success. At the end, I deleted the query, and recreated it again and
now it works. I compared property settings, but as the query is
actually inherited from an ancestor class, property settings are in 3-
4 different files (this is one thing I really hate in Delphi...)

Thanks for the support (special thanks to Hellen)