are there any exceptions(cases) that glibc is not strict backward-compatibility?

[Jason Yang]

Dear developers:

I am curious that are there any cases(exceptions) that we need to notice 
in terms of glibc backward-compatibility?

I mean glibc is not 100% percentage backward-compatibility, there should 
be some cases(exceptions) we need to care about when we use glibc to 
implement our own libraries, right?

Where can I find these exceptions?


Regards,

Jason