Stata: clttest command gives me different results every time

I am running something like

clttest truth, cluster(userid) by(envyfree)


and every time I run the command I get different results, which is super shady. Truth and envyfree are 0-1 variables. Any possible explanations would be most helpful. ​​​​​​​ I attach two figures showing the different results:

Haven't used stata, but in R there is there is a function called set.seed. What this does is seeds a random number generator, meaning any result from random data can be replicated http://rfunction.com/archives/62.