Warning: sieve: file storage: Active sieve script symlink is broken: Invalid/unknown path to storage

Mon Mar 16 17:08:00 UTC 2015

dovecot version:
2.2.16 (3d8a054a93a9)

sieve configuration:
plugin {
  sieve = ~/.dovecot.sieve
  sieve_dir = ~/sieve
 }

For each of the users, ~/.dovecot.sieve is a symlink to
~/sieve/roundcube.sieve

Until yesterday, everything was working find. But starting from yesterday's
update, the log is filling up with messages like:
Mar 16 19:12:32 cs12986 dovecot: lda(postmaster at contoso.com
<postmaster at euro-contact.ru>): Warning: sieve: file storage: Active sieve
script symlink /home/virtualmail/contoso.com/it/.dovecot.sieve
<http://euct.ru/it/.dovecot.sieve> is broken: Invalid/unknown path to
storage (points to /home/virtualmail/contoso.com/it/sieve
<http://euct.ru/it/sieve>).

Nothing was changed in the config files.

What might have gone wrong?