Placeholder should be shown when the entry is focused
Submitted by Mounir Lamouri
GtkEntry documentation  has this note about placeholder: "Note that since the placeholder text gets removed when the entry received focus, using this feature is a bit problematic if the entry is given the initial focus in a window. Sometimes this can be worked around by delaying the initial focus setting until the first key event arrives."
The reason why the placeholder isn't shown when the entry is focused is not given; the only reason given is why it should be shown. It sounds like this note is a pretty good reason to have the placeholder shown when the entry is focused. FWIW, this is what Mac OS and Windows seem to do.