IMAP error when searching for a non-ASCII string (russian)

[DSV12]

G'day for all!

After upgrading roundcube to 1.6.12 (1.6.13, 1.6.14, too) we can't do serching in folders in Russian (non ASCII symbols).

Server error: UID THREAD: Error in IMAP command UID THREAD: Missing LF after literal size (0.001 + 0.000 secs).

Search is only possible in English (ASCII). Where error from?