I haven't seen this reported before. I have noticed when creating a sheet worker with any _max attribute, it does not create the newValue and previousValue properties.
For example, create two inputs, textareas, or spans, one for the normal attribute, and one for the _max attribute
<textarea name="attr_example" ></textarea>
<textarea name="attr_example_max" ></textarea>
Then create a simple sheet worker
on('change:example change:example_max', event => {
console.log(event);
})
Then enter anything in the example box, both example, and example _max events fire (as normal), but their contents are different:
If you enter anything in the _max box, you see the same thing.
The lack of a value in the _max box means it is impossible to caclulate the magnitude of changes, or the direction of changes. This is important stuff!