When it comes to placing glyph's in the Private Use Area I get mixed opinions from people, some say never place any glyph in the PUA because it could cause a problem however they can't tell me what type of problem or they'll say I don't know someone else told me not to.
If alternate glyph's are left unmapped with out unicode values then very few third party character maps will be able to access the alternate glyph's, Adobe products will show them but there's applications that wont see them which makes my font less usable.
What are the potential problems of placing glyph's in the PUA?
If not the first PUA can alternate glyph's be placed in one of the supplementary PUA's?
Thanks for any reply.