Replace text and insert text edits transposed

I am editing a PDF in Adobe Acrobat Pro DC, v. 2015.020.20042, on Mac OS 10.11.6

When I attempt to replace text by selecting and then typing, or when I attempt to insert text by typing at the cursor, the first two letters that I type are transposed in the comment box.

Every.

Single.

Time.

If I type more than two letters, the intended first letter gets pushed to the end. For example, if I type the correction, "Ah," I get "hA" in the comment box. If I type "Hah," the result is "ahH".

I've noted this problem in earlier versions but haven't edited a PDF in almost a year. No doubt there is something about my particular set-up that is conflicting with Acrobat, but I can't believe I'm the only one.

I have 96 edits remaining in the document. Thanks, Adobe.