A set of random draws is less smooth or regular than many people expect. So the behavior you report is to be expected and is desirable.
There are special circumstances where you may want something more regular than a random draw, e.g. when using maximum simulated likelihood. For those situations one option is to use a Halton set, see -help mf_halton- and the special issue of the Stata Journal on maximum simulated likelihood: http://www.stata-journal.com/s...