No beta coefficitents available when using regress with cluster option: Why?

This question has already been asked on statalist but there is no satisfying answer to it yet.

When you want to get the standardized coefficients you are usually allowed to add the option -beta- to the regress command in stata. However this does not work when you use the option -cluster(group)- to adjust the VCE for cluster correlated disturbances.

What is the reason for this and is it allowed to calculate the standardized coefficients by hand in this case?