In what aspect C++ support in bison is nowhere near as mature as the C support?

[Peng Yu]

In Levine' flex & bison book, it mentioned "As should be apparent by
now, the C++ support in bison is nowhere near as mature as the C
support,..." on page 241 (Chapter 9).

I'm still learning bison and haven't finish reading all the previous
chapters. Could somebody point to me explicitly in what aspects C++
support is not as mature as C support?

Are there any features that C++ support is better than C support? (I
know C++ location is better according to the book, anything else?)