Copter-4.1.5 has been released as the official/stable version and can be installed using your favourite ground station (MP, QGC, etc) or downloaded directly from firmware.ardupilot.org.
This is a relatively small release with just two changes listed below (and also in the ReleaseNotes):
Changes from 4.1.4
Bug fixes
a) attitude control I-term always reset when landed (previously only reset after spool down)
b) revert SBUS RC frame gap change from 4.1.4
Thank you for your great work, what about this warning, has it been resolved? " WARNING: we have a report that FrSky R9 receivers are not detected because of (3j) so if you are using these receivers please remain on 4.1.3 for now.
As you can see from the release notes above, the calibration code has not changed. So it is most probably a hardware issue. Is the copter hardware 100% identical? Or are they different? What are the differences?