It's that "well known" I'd never heard it before
I think it's much more likely that there have been literally too many submissions for build slots at the BMW factory and they can't keep up. Dealers give the standard 6-8 weeks timeframe to the lease companies and then when BMW actually sort their factory out they find they've got way too many orders for 6cyl diesels and they can't keep up.
That's my best guess
