If you go to Compute->MachineSets->Hamburger on a machineset->Edit Counts you can click the minus button until it goes negative. It should probably stop decreasing at 0.
I'm also told those buttons are not keyboard or screen reader accessible, if you can fix that while you are in there :)
machineset->Edit Counts the minus button will disabled when count is zero
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.