I've found this article on Internet about it: http://www.suse.de/~agruen/acl/linux-acls/online/

Most UNIX-like systems that support ACLs limit the number of ACL entries allowed to some reasonable number. Table 3 shows the limits on Linux.

Table: Maximum Number of Supported ACL Entries File system Max. entries
XFS 25
Ext2, Ext3 32
ReiserFS, JFS 8191

ACLs with a high number of ACL entries tend to become more difficult to manage. More than a handful of ACL entries are usually an indication of bad application design. In most such cases, it makes more sense to make better use of groups instead of bloating ACLs.
I'll see what I can do about it.