Is this a new rule in the current CBA?

[lbgreen33]

Pat Riley signed with Miami Heat while he still had a year remaining on his contract with the Knicks.  The matter was settled after the Heat sent their 1996 first round pick and $1 million in cash to the Knicks.  Is there a new rule in the current CBA that says you can't do this anymore?  Why would Danny say he wanted a pick for Doc if you can not do it anymore?  Just wondering if anyone knows the rule.