Steam requests accessibility access in OS X

When I start OTC, Steam always pops up this dialog box saying it needs game overlay access even though it already has rights in the system prefs. I can click 'ok' and continue normally, but it's a minor annoyance. Trying to add the Offworld Trading Company.app itself doesn't work; when I try to add it to the list in the prefs panel it doesn't appear. Other Steam games that use the overlay don't have this problem.

OS X 10.10.2

OTC .4853