While I didn't run any tests, my best guess is, all dependent packages should work with the new ABI. With Jack, only the exposed C API is expected to be stable and used by applications. The C++ API change, that you are seeing in the ABI test, is supposed to be internal. Not sure why these headers are exposed in the devel package.
Thank you. This solves the half page printing issue.
I independently confirmed that 1.6.5 does not solve the segfault problem.