Can't assign new leave policy to employee

[kombi]

Employee x has leave policy y containing only privileged leave¹². When I try to assign leave policy z containing also compensatory leave, erpnext gives me "already assigned"³ when in fact it is not.

Here are some screenshots:

1. Employee 9 has assignmend 9:
   

   

2. In it is leave policy 1:

3. When trying to assign leave policy 4 I get this:
   

What might I be doing or getting wrong?