This airport, KMKO, Muskogee-Davis Regional in Oklahoma southeast of Tulsa is depicted on the sectional chart with symbology normally reserved for airport with a hard surfaced runway longer than 8069 feet, but this one is only reported on the sectional as 7200.
Is this a mistake by the FAA or is there some clear explanation about why this is?
A FAA chart user's guide diz:
Hard-surfaced runways greater than 8069' or some multiple runways less than 8069'
It's the latter case of some multiple runways less than 8069'.
This is also confirmed in the post, "What is significant about the number 8069 ft?"
Specialists also place these polygons around the runway pattern of aerodromes with multiple runways that are less than 8069 feet, in cases where the multiple runway pattern does not fit into the largest, circular aerodrome symbol.
(FAA FAQ; emphasis mine.)
Most likely MKO doesn't fit in the standard circle 
because of 36-18 and/or 4-22 intersecting the circumference.
(Chart Supplement via skyvector.com)