Bug#791067: Is this a general ban on soname bumps with gcc5 transitions, or just hdf5?

[Rebecca N. Palmer]

New gcc5 transition notices are still being sent out with the "Such a 
change can be avoided, if you have a soversion bump and you upload this 
version instead of the renamed package" wording (e.g. simgear 
https://bugs.debian.org/797944 ); is this a mistake, or is hdf5 special 
because it has both C and C++ interfaces (so a soname bump would drag in 
C rdeps that wouldn't otherwise be affected) and a fairly large number 
of rdeps?