I tried this for HSA and hsa, which are acronyms I use often.
Both still get auto-corrected to HAS and has.

I also tried putting them in the autocorrect exceptions "Other Corrections" list. Entering HSA in the input box converts instantly to lower case hsa in the list after you click Add. It appears not to be possible to enter an all caps word/acronym. Hit all the OKs to get out of dialog boxes and save. hsa still gets autocorrected to has every time.

And I have tried exiting and restarting outlook and word after making the above changes. Still autocorrects hsa to has.

Using Office 2010 on Windows 7.
See the same issue on two different machines.

Any idea what is going on here?