Screenlets do not re-open on the same desktop

This is not exactly a bug, because for now the screenlets simply not remember on which desktop they were started. It was always up to discussion if it isn't instead the window manager's job to set preferred positions on certain windows (especially since we never can safely assume multiple desktops to exist). But I'll add this to the wishlist, since I agree that this is a required improvement and it can't hurt to have the screenlets remember their workspace/desktop number.

You can use gDevilsspie/Devilspie to partly fix it, creating a rule for your Screenlet like this:

( if
( begin
( contains ( application_name ) "Screenlet.py" )
)
( begin
( set_viewport 3 )
( println "match" )
)
)

However, it does not work when Screenlets are cloned from a service, if I unerstand it correctly. And you can always make a Screenlet "Sticky" in order to make it appear on all workspaces.