Version: IE10 for Windows 7 (10.0.9200.15521)
As per the subject, the spellcheck component is completely inoperable for any user that has their AppData directory redirected to a UNC path. The spellcheck does not mark misspellings or suggest corrections, and has broken UI elements in the Manage Add-ons dialog.
I can reproduce this on any account for which folder redirection is enabled on my domain, including administrator accounts. A screenshot of the UI problem, along with further explanatory details on the issue, is posted at: