Even though you export the solution as managed and then import it into the same organization, all the changes, which have made to the organization do not revert back.
Example:
1. Create a publisher and a solution.
2. Open the solution and do customizations, like adding Entities, adding Fields, removing values from OptionSet.
3. Export the solution as managed, delete the unmanaged solution and install the managed solution to the same organization.
4. Now uninstall the solution, expecting all the customizations have been removed to make the organization in a default state.
Results:
All the modification still remains. The objects you created as still in the organization and values which has been removed has not revert back.
Example:
1. Create a publisher and a solution.
2. Open the solution and do customizations, like adding Entities, adding Fields, removing values from OptionSet.
3. Export the solution as managed, delete the unmanaged solution and install the managed solution to the same organization.
4. Now uninstall the solution, expecting all the customizations have been removed to make the organization in a default state.
Results:
All the modification still remains. The objects you created as still in the organization and values which has been removed has not revert back.