incorrect -a flag in busybox tar (creation mode)?

[David Demelier]

Hello,

I've discovered that busybox tar -a flag acts differently than both 
bsdtar and GNU tar. If the archive ends with extension .txz it creates a 
LZMA file rather than xz.

See:

$ bsdtar caf ../MANIFEST.txz *
$ file ../MANIFEST.txz
../MANIFEST.txz: XZ compressed data
$ tar caf ../MANIFEST.txz *
$ file ../MANIFEST.txz
../MANIFEST.txz: XZ compressed data
$ busybox tar caf ../MANIFEST.txz *
$ file ../MANIFEST.txz
../MANIFEST.txz: LZMA compressed data, streamed   (<- why?)

Is there a bug in busybox tar -a flag or I miss something?

busybox 1.30.1
GNU tar 1.29
bsdtar 3.2.1 - libarchive 3.2.1 zlib/1.2.8 liblzma/5.2.2 bz2lib/1.0.6


Regards,

-- 
David