1. create Job A
2. create Job B
3. configure Job A with a build step the that blocks until trigger for parameterized job B completes,  
4. configure Job A with a dynamic parameter with following groovy:

println "JOB PARAMETER"
return [1,2,3]

1. configure Job A with a promotion when... Job B is successful
2. build the job
3. check jenkins logs for "JOB PARAMETER"  take note of the count.  i.e.  grep "JOB PARAMETER" /var/log/jenkins/jenkins.log | wc -l
4. click Build with parameters for Job A agains
5. check jenkins logs for "JOB PARAMETER"  take note of the count2.  i.e.  grep "JOB PARAMETER" /var/log/jenkins/jenkins.log | wc -l
6. difference should be 1 however it's 4.

the more blocking jobs you add to Job A the promotion job call generation of parameters many times over for each static job.   
this in turn is leading to a lenghty load time to several of our jobs that make a webservice call of the paramters and the job has about 7 static downstream jobs and the paramter generation happens about 120 times per job load or build click.