Permanent links to custom commands

I cannot figure out how to maintain permanent links to particular custom commands. Steps to reproduce:

1. Define two custom commands in Webmin (1.410) on one system. The internal Webmin links to these commands end with e.g. edit_cmd.cgi?idx=0 and edit_cmd.cgi?idx=1
2. Now take the contents of e.g. /etc/webmin/custom and copy it over to a handful of systems, all running the same OS and software, same versions of Webmin and Virtualmin etc etc.
3. On some systems, the links are shuffled. The first command becomes '1' and the second command becomes '0', i.e. reversed compared to the original system. On the rest of the systems, the numbering is the same as per the original.

I can't figure any pattern at all. Seems totally random.