LDAP servers that strictly check may not allow aliases with additional attributes (see e.g. openldap Issue #3017).
This is a definite problem if you actually want to use an alias which uses a name component taken from the aliased object - the common case - in fact, jxplorer itself tries to use the name attribute from the object being aliased. So, the Done Thing these days seems to be to include the extensibleObject as well as the alias objectClass when creating an alias. The attached trivial patch adds an option to add extensibleObject objectClass when using "paste alias" to jxplorer. It is handy!