instances() collects all versions of mutable variables

[Freewalkr]

I'm not sure if this is not an expected behavior, so posting this to discussions:
Schema.instances() function returns all versions of mutable variable if it was mutated. Minimal example:

schema MutateMe:
    things: [str] = []

_m = MutateMe {}
_m.things += ["thing"]
m = MutateMe.instances()

This renders to:

m:
- things: []
- things:
  - thing

Is this an expected behavior? If so, shouldn't there be a flag for instances() to collect only immutable instances of schema? I'd like to have some way to get only the last version of mutable variables for the code above to render like this:

m:
- things:
  - thing