fixes serveral bugs in routine get_async in basic interpolation operations

Summary

In the !420 (merged) the latest changes fixed a couple of bugs in basic interpolation operations. Even though the MR is not yet completed, I would like to merge back the intermediate stage into the master.

Checklist

• All code changes are covered by unit tests
• Code coverage did not deteriorate
• Code follows Style Guide
• Documentation updated, if necessary
• Update version info, if changes are worth mentioning (Develop section in doc/src/version_info.dox, add section if not yet included)