We're using poky 2.5.1, bitbake version reports:

bitbake --version
BitBake Build Tool Core version 1.38.0

We have a msmtp_%.bbappend where we modify pkg_postinst_ontarget by appending to it:

pkg_postinst_ontarget_${PN}_append() {
    killall -9 inotifyd || true
}

I am observing that changes in pkg_postinst_ontarget_${PN}_append() are not being picked up in incremental builds, i.e. I can change the line in the ontarget append function and the package is not being rebuilt.

If I cleanall the package and build it again, then my changes are there.

We are using prserv in our setup and for instance, changes in do_install_append() cause a rebuild an a prserv initiated pr bump, but changes in pkg_postinst_ontarget_${PN}_append() seem to be ignored. I can easily and consistently reproduce it in my setup.

It's worth mentioning, that when I run bitbake -e msmtp and look for pkg_postinst_ontarget_msmtp= in the output, then I do see my changes there.