proftpd mod_auth_file fails with crypt(3): Invalid argument

[Mario Emmenlauer]

I use for authentication in proftpd the mod_auth_file. This used to work well with proftpd-basic (1.3.2c-1ubuntu0.1) from lucid-updates, but fails with proftpd-basic (1.3.5~rc3-2.1ubuntu2) for the same setup. The error in proftpd logfile is

mod_auth_file/1.0: error using crypt(3): Invalid argument

Here the relevant section from my config file:
AuthOrder mod_auth_file.c
AuthGroupFile /home/www/configsystem/proftpd.group.passwd
AuthUserFile /home/www/configsystem/proftpd.user.passwd

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: proftpd-basic 1.3.5~rc3-2.1ubuntu2
ProcVersionSignature: Ubuntu 3.13.0-49.81-generic 3.13.11-ckt17
Uname: Linux 3.13.0-49-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.8
Architecture: amd64
Date: Fri Apr 10 00:49:09 2015
SourcePackage: proftpd-dfsg
UpgradeStatus: Upgraded to trusty on 2015-04-09 (0 days ago)
mtime.conffile..etc.default.proftpd: 2015-04-10T00:16:51.463030
mtime.conffile..etc.init.d.proftpd: 2015-04-09T23:54:08.146334

[Mario Emmenlauer (emmenlau)]

I've tested several older versions of proftpd on trusty now, all with the same error message. So the problem might not originate in proftpd, but rather in another library. With google I found various references that supposedly the behavior of crypt has changed sometime ago. Could this be related? See for example:
http://patchwork.openembedded.org/patch/47529/

[Mario Emmenlauer (emmenlau)]

Can not reproduce after regenerating password.