[Help] Cyrus 2.4.17 segfault

[Marco]

Hello,

  we are experiencing a strange problem on cyrus-imapd 2.4.17.

An user user/a has full ACL to another mailbox user/b. When the user/a 
SELECT a folder on user/b where he has access the imap process crashes.

$ telnet cyrus.example.com 143
Trying 10.10.10.10 ...
Connected to cyrus.example.com.
Escape character is '^]'.
* OK [CAPABILITY IMAP4rev1 LITERAL+ ID ENABLE AUTH=PLAIN SASL-IR] 
cyrus.example.com Cyrus IMAP v2.4.17-Invoca-RPM-2.4.17-6.el6 server ready
a authenticate plain dsfrrFwaWNlQGNzaS5pdABveGN5cnVzAENdfsdfMx
a OK [CAPABILITY IMAP4rev1 LITERAL+ ID ENABLE ACL RIGHTS=kxte QUOTA 
MAILBOX-REFERRALS NAMESPACE UIDPLUS NO_ATOMIC_RENAME UNSELECT CHILDREN 
MULTIAPPEND BINARY CATENATE CONDSTORE ESEARCH SORT SORT=MODSEQ 
SORT=DISPLAY THREAD=ORDEREDSUBJECT THREAD=REFERENCES ANNOTATEMORE 
LIST-EXTENDED WITHIN QRESYNC SCAN XLIST URLAUTH URLAUTH=BINARY 
X-NETSCAPE LOGINDISABLED COMPRESS=DEFLATE IDLE] Success (no protection) 
SESSIONID=<cyrus-4400-1573486341-1>
a SELECT "user/b/SOME THINGS/WATER"
Connection closed by foreign host.


Could you suggest me some way to resolve this problem?

I have already tried "reconstruct -rf" on user/a and user/b and 
ctl_cyrusdb -r without success.

Thank you very much for every hints

Marco