Raimey,

this is an interesting topic!
I have in front of me a little book published by the hunting museum in Ohrada, in Hluboka nad Vltavou, Czech Republic - by the way a place recommended to visit, an interesting collection on hunting, fishing, forestry, and many fine hunting guns, focussing on Bohemia and Movaria.

Sorry I can't copy pictures from this book, but I see these stepped locks in quite some guns:

two different 4-barrel percussion rifles signed A.V. Lebeda a Prague
a percussion double rifle also by A.V. Lebeda
a percussion double rifle signed K. Haberda in Frauenberg (this is Hluboka nad Vltavou!)
another percussion double signed F. Ludykar in Wittingau (this is Trebon, quite close to Hluboka - both in the area of Ceske Budejovice, not far from the Austrian border)
a single shot percussion rifle by F. Nowak in Prag
a single shot percussion rifle by K. Haberda in Frauenberg
a percussion target rifle by J. Anton Kuchenreuter in Regensburg, Bavaria
a double shotgun by C.G. Koenig & Sohn in Coburg
(those last three with locks with the spring in front of the hammer, but nevertheless a small step at the back of the action plate)

No earlier flintlocks or later centerfire guns shown with this "step", seems to be a percussion-time fashion.
Created in Bohemia or somewhere around, my first guess would be Lebeda in Praguue.

Best regards,
fuhrmann