Use tinymce from tinycme package instead of the shipped one.
---- roundcube-0.1~rc2.orig/program/steps/mail/sendmail.inc 2007-11-26 11:42:36.000000000 +0100
-+++ roundcube-0.1~rc2/program/steps/mail/sendmail.inc 2007-11-26 11:44:04.000000000 +0100
-@@ -123,7 +123,7 @@
+Index: b/program/steps/mail/sendmail.inc
+===================================================================
+--- a/program/steps/mail/sendmail.inc 2009-10-14 12:52:27.000000000 +0200
++++ b/program/steps/mail/sendmail.inc 2010-07-17 17:33:23.000000000 +0200
+@@ -115,7 +115,7 @@
// sanitize image name so resulting attachment doesn't leave images dir
$image_name = preg_replace('/[^a-zA-Z0-9_\.\-]/i', '', $image_name);