Why would you deduce that it is the Perl CORE at fault?
I didn't: It's not my bug. The conclusion was that the 5.10 installation as whole held some incompatibility. I agree the slippery XML parser is a likely culprit (and a serious pain), possibly because the "wrong" one is already pre-installed(?) for the OS.
using Perl since 1995 and have *never* encountered incompatibilities
going forward.
See the "Incompatible Changes" section of perldelta for any release, including the current one:
Perl is still a model to me of how things should go, but the number of times it has been necessary to break compatibility is non-zero.
--joe