Even though I tried very hard I unfortunately cannot provide steps to replicate this erroneous behaviour. But it happened to me here and there.
The tooling provides a way to have a specified number of pods for a service. This is available via the context menu of a service (and other items in the tree and in the properties).

The dialog that allows you to scale the number of replicas to a specific number initially shows the current number of replicas. You can then provide a specific number of replicas that you want to have, enabling the "OK" button.