Further and finer analysis by Kurt Hornik of the upstream R Core team suggests that only the 3.5.1-1+b2 seems to be affected. Re-reading I see that Pavel already said so -- my apologies for missing that the first time around.
I think I'll just build and ship a fresh 3.5.1-2 which should take care of this. Thanks, Dirk -- http://dirk.eddelbuettel.com | @eddelbuettel | e...@debian.org