how do you know which python egg is enforcing a constraint in buildout?

For instance the following is built with bin/buildout -Nvv

...
Getting required 'grokcore.component>=2.5'
  required by five.grok 1.3.2.
  required by grokcore.viewlet 1.11.
Picked: grokcore.component = 2.5
Getting required 'grokcore.annotation'
  required by five.grok 1.3.2.
Picked: grokcore.annotation = 1.3
The constraint, 0.4, is not consistent with the requirement, 'five.localsitemanager>2.0dev'.
While:
  Installing instance.
Error: Bad constraint 0.4 five.localsitemanager>2.0dev

The constraint five.localsitemanager>2.0dev does not seem to be enforced by grokcore.annotation (see https://github.com/zopefoundation/grokcore.annotation/blob/master/setup.py) But how do I find out which egg is actually enforcing this?