Has anyone discovered spelling errors when transferring changes from Acrobat Pro back to InDesign, the original program?

Haven't experienced that myself, but it sounds like something may be going wrong during the import of the PDF corrections back into InDesign. Doublecheck that you're using the latest versions of both Acrobat Pro and InDesign, and compare the imported changes against the original PDF to see exactly where the spelling errors are being introduced. If it happens consistently, it may be worth testing with a smaller document to see if the issue is reproducible. That can also help determine whether it's a workflow issue or a bug.