It seems that if a GET has text in it and you want to edit it the text always gets added to the end or the beginning regardless of whether or not you have double clicked the mouse to a desired insertion point or blocked part or all of the test to overwrite / replace.
This can be seen with testdlg.prg if you initialise cAddress to some value, for example:
local cAddress := "My Address "
rather than set it to SPACE(20).
I note also that I have received the following warning which may or may not be related to the above problem:
(<unknown>:26188): Gtk-WARNING **: GtkEntry - did not receive focus-out-event. If you
connect a handler to this signal, it must return
FALSE so the entry gets the event as well
Didn't notice that from my code but did from testdlg.prg with initialised cAddress,