From a cursory look into Illuminate\\Database\\Eloquent\\Model
I can see the following instance attributes:
protected $connection
protected $tab
It appears that $changes
is also a reserved name.
These attributes can not be static because they are used as their model configuration. If you rewrites them in your model class, you define your own parameters, if not, the Eloquent believes it should use the defaults. Yes, you should not have a column name in your table that matches the name of one of these attributes.