Mysql 4.1.14 as well as 4.1.18 (at least) contains a bug very similar to http://bugs.mysql.com/bug.php?id=11892. Applying the attached patch (which is basically the one applied on the 5.0 : http://lists.mysql.com/internals/32932) solved it. Could it be added to the mysql 4.1.x ebuilds ?
Created attachment 84910 [details, diff] proposed patch Changeset http://lists.mysql.com/internals/32932, but applied on a mysql 4.1.14
4.1.20 is in the tree ... closing