I think they can be troublesome because depending on what they are and how counter-intuitive they are, they can be more work than they are worth. I'm reminded of a girl I went to school with who tried to insist people call her "Ten" (her name was
Kristen. Get it? Yeah).
I think the main problem with the examples you give is that the nicknames are first and most strongly associated with totally separate names. A
Ron will automatically be thought of as a
Ronald. A
Poppy with be thought of as a
Poppy before
Penelope. It might make people wonder, if you liked
Ron so much, why not call him
Ronald in the first place?
All that being said I don't really have a problem with such names. I do think that if one wants to use such a name though, one should not get huffy when people don't call
Cameron "
Ron" automatically or even put up some resistance with that choice.
I have a few more-obscure nicknames on my lists, let me see:
Babs for
Barbara, but I also like it as an option for
BlancheSolly for
SolomonTolly for
BartholomewKathe for
KatherineNils,
Nels and
Cole for
NicholasHob and
Hopkin for
RobertSasha for
AlexanderDiot and
Dye for
DionisiaIbb and Ibby for
IsabelJoyce for
Jocosa or
JocastaMack for
MagnusMattie or
Matty for
MarthaTenney for
DennisWilky for
William