Bound but also not bound to be unreliable (4,3,5)
I believe the answer is:
fast and loose
'be unreliable' is the definition.
(thesaurus)
'bound but also not bound' is the wordplay.
'bound but' becomes 'fast' (I can't explain this - if you can you should give a lot more credence to this answer).
'also' becomes 'and' (both can mean in addition).
'not bound' becomes 'loose' (I've seen this before).
'fast'+'and'+'loose'='FAST AND LOOSE'
'to' is the link.
Can you help me to learn more?
(Other definitions for fast and loose that I've seen before include "Lacking in moral obligation - old cheating game" , "How one trifles with" .)