dsync panic

[Infoomatic]

Hi,
I just upgraded from dovecot 2.2.19 to 2.3.2. "doveadm backup" worked fine in v 2.2.19, but now panics (user with shared folder):
/opt/dovecot/bin/doveadm backup -u testuser -1 sdbox:/tmp/testuser

dsync(standl2): Panic: file mailbox-attribute.c: line 360 (mailbox_attribute_get_stream): assertion failed: (value_r->value != NULL || value_r->value_stream != NULL)
dsync(standl2): Error: Raw backtrace: /opt/dovecot/lib/dovecot/libdovecot.so.0(+0xcb6fa) [0x7f43679986fa] -> /opt/dovecot/lib/dovecot/libdovecot.so.0(+0xcb769) [0x7f4367998769] -> /opt/dovecot/lib/dovecot/libdovecot.so.0(i_fatal+0) [0x7f43679069c1] -> /opt/dovecot/lib/dovecot/libdovecot-storage.so.0(+0x568ff) [0x7f4367c9d8ff] -> /opt/dovecot/bin/doveadm(dsync_mailbox_import_attribute+0x4d) [0x56234f7b68dd] -> /opt/dovecot/bin/doveadm(dsync_brain_sync_mails+0x2fd) [0x56234f7b217d] -> /opt/dovecot/bin/doveadm(dsync_brain_run+0x538) [0x56234f7adb28] -> /opt/dovecot/bin/doveadm(+0x27fec) [0x56234f793fec] -> /opt/dovecot/bin/doveadm(+0x2a0e7) [0x56234f7960e7] -> /opt/dovecot/bin/doveadm(+0x2ad7b) [0x56234f796d7b] -> /opt/dovecot/bin/doveadm(doveadm_mail_try_run+0x1fa) [0x56234f79769a] -> /opt/dovecot/bin/doveadm(main+0x45b) [0x56234f786b2b] -> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0) [0x7f4367523830] -> /opt/dovecot/bin/doveadm(_start+0x29) [0x56234f786ca9]

regards,
infoomatic