Hitler the Artist
Critical Inquiry, Vol. 23, No. 2 (Winter, 1997), pp. 270-297
I have not looked into this very far. This article is by far the most enlightening I've seen. It establishes that Hitler's occupation (prior to mass murderer) was fine artist.
There's a lot of documentation here about how and why Hitler was lampooned as an uneducated housepainter (mainly, this was a minor political strategy of his opponents in Munich). Apparently, the leap from painter to paperhanger was made because of the allied nature of the trades.
Somewhat surprisingly, the man most responsible for the canard seems to be Bertolt Brecht. The poet was a longtime antagonist and made regular references to Hitler's political treachery. Brecht portrayed Hitler whitewashing the exterior and fooling others into complacency and trust; yet all the while the integrity of the wall was crumbling away.
Some translation considerations may have come into play. The image of whitewashing (in order to conceal something less wholesome) is not far removed from the image of papering over a problem.
Here's a link to Arthur Mitchell's 2007 account.