ZID Controller described a near MOA incursion event that reportedly was caused when navigational information was entered into the aircraft FMS. The reporter noted that this same anomaly has occurred in the past.

Narrative

An MD88 departed CMH southbound. Buckeye MOA was active as well as the Charlie shelf refueling track. The MD88 was assigned a 160 heading by CMH Approach to avoid the Buckeye MOA. Trainee climbed the aircraft to 17;000 FT and fly present heading to join J186. Pilot read back clearance correctly. A few minutes later; I noticed that the MD88 had turned south before joining the jet route and was about to enter the active MOA airspace. I turned the MD88 to the east to avoid the airspace. Pilot deviation information was then read to the pilot.This exact same pilot deviation has occurred before. The pilots claim that their FMS turns them direct the next fix on J186 (OHIOS) before joining the airway. This is a very; very dangerous situation. I don't know what the pilots need to do to avoid this happening in the future; but we can fix this issue by adding a fix on J186 that is 5 miles north of the Charlie shelf on J186. This will give us a fix for the aircraft to join J186 and avoid the buckeye. This fix can also be used as a crossing point to allow us to climb the higher performance aircraft above the Charlie shelf (i.e. cross XXXXX at FL230). Charlie shelf is normally active FL190-FL220.