Instanceof behaviors broken when querying a container class in the same session

### Task List

- [x] Steps to reproduce provided
- [x] Stacktrace (if present) provided
- [x] Example that reproduces the problem uploaded to Github
- [x] Full description of the issue provided (see below)

### Steps to Reproduce

In the context of the sample project, we have a "Drawing" entity that contains a "Shape" entity. "Shape" is sub-typed to "Circle" in this case.

1. In a session, query the "Drawing" table using any method (where queries, finders, etc)
2. Attempt to use `instanceof` on a "Shape" instance from the table

### Expected Behaviour

The shape instance should be `instanceof` Circle.

### Actual Behaviour

`instanceof Circle` returns false

### Environment Information

- **Operating System**: Fedora Linux Workstation 28
- **GORM Version:** 6.1.10.RELEASE, 6.0.12.RELEASE
- **Grails Version (if using Grails):** 3.2.13
- **JDK Version:** openjdk version "1.8.0_181"

### Example Application

- https://github.com/joemccall86/gorm-upgrade-instof

Start by running the linked gorm-upgrade-instof example application and inspect how Drawing, Shape, and Circle are mapped and queried in the same session. Reproduce the query, trace the returned Shape instance, and verify that it is recognized as an instance of Circle without breaking other inheritance behavior.

Written by the indexing model from the issue text.