Labor improdus omnia vincit

This is the motto of Fond de l'étang - a boarding school for wayward boys in post-WWII France and the setting for Les Choristes, a 2004 French film directed by Christophe Barratier. A couple years ago I bought a DVD to watch with my French classes on the recommendation of my son who had spent a year in France a decade ago as a foreign exchange student. The motto - in large capital letters - appears one time in the film on a wall in a hall of the building as the new master is introduced to the place. Beneath the Latin and at the right is the ascription "Vergile".

Why is this motto so laughably mistaken? Vergil says in his Georgics I.145-6:

. . . labor omnia uicit 145

improbus et duris urgens in rebus egestas.

A troublesome sentence to comprehend although not terribly difficult in vocabulary and syntax.

At the Erreurs de Films page on this movie appears this comment by "Michel B":

La devise du 'fond de l'étang', apparaît à un certain moment : 'labor improdus omnia vincit' ne signifie rien en latin. Il faut lire 'improbus' et non 'improdus' (Barbarisme).

Possibly the error is intentional. The phrase in the motto has been around a good while. It produces at least 250 hits on Google (mostly European), among which appear glosses like this: Un travail opiniâtre vient à bout de tout. E.g. from the Institute of Physiology and Pathology of Hearing:

Officer's Cross "Labor Improdus Omnia Vincit" for scientific achievements of the Institute of Physiology and Pathology of Hearing, awarded at the 57th World Exhibition on Innovation, Research and New Technologies INNOVA 2008

It seems to have been adopted as a tag-line by somebody going under the name "Gael" in a French listserv of some sort called Forum des Coquillards de Villon. You can see a representative post here. Of course, a goodly number - perhaps most - of the postings since 2004 may be parroting this film, wittingly or not, though it seems doubtful that the Officer's Cross thing derives from the movie, or at least from this version of the movie.

By contrast, the less incorrect "Labor improbus omnia vincit" produces some 18,000 hits on Google, and the shorter version (omitting the problematic attributive adjective) "Labor omnia vincit" some 67,000.

Perhaps the director or possibly the screenwriters (Barratier and Philippe Lopes-Curval, who were adapting the 1947 film La Cage aux Rossignols) have included this bit as a subtle - or not so subtle - comment on the pretensions of this internat de rééducation réservé aux enfants en difficulté. Throughout the film representatives of the school's administration confidently babble in (then) current psycho-socio-educational buzz-words, but they cannot even get a simple Latin quotation right on their proudly displayed motto. Rather, with a complete lack of genuine discernment, they latch onto some debased Latinate hard-work-is-good-for-you proverb floating around here or there and paste it up where it will impress the hoi polloi.

Perhaps it even goes further with a gentle but telling cut at the growing shallowness of a society coming adrift from its cultural roots. After all, nobody in the film comments on the error, or even appears to notice it. Nobody's education has included enough time with one of the preeminent writers of antiquity to recognize a misquote prominently displayed on the wall.

On the other hand, this may have appeared in the earlier film and simply been copied. In that case, we are back to wondering the same things about those involved in that earlier production.

Or is the real answer, as "Michel B" suggests, that these film people (whether in the later or the earlier or both versions of the story) just wanted a Latin motto saying something about the value of work and were too hasty and too cheap to get it right.