Lowering buttons when pressed (FvwmButtons)

I have made som buttons in my FvwmButtons bar. When I press these buttons (Icons) they get lowered for at split second:

*FvwmDock: (28x5, Frame 1,Icon "knode.png", Action (Mouse 1) Exec exec knode)

*FvwmDock: (28x5, Frame 1,Icon "konqueror.png", Action (Mouse 1) Exec exec konqueror)

But when I press this button (that swallows xlassie) nothing happens:

*FvwmDock: (28x5, Frame 1, Swallow(Respawn) "xlassie" "Exec exec xlassie -spool /var/mail/me -clickcommand kmail -bell -hilight -bg gray")

Is there someway to make this swallowed button change when pressed?

That’s because the button you’re pressing doesn’t launch anything – the click is passed directly to Xlassie, which then runs whatever you tell it.

– Thomas Adam

Is there any way around this or is it impossible to make it change when pressed because the click is only noticed by xlassie?