If it was it the eqivilant of a shut door respray, maybe the painters didn't strip all the bits off the roof before painting.. In which case they may have simply removed the antenna and masked the plastic part (along with other parts) where some paint got into the screw thread...
If so unscrew the antenna and check the that base antenna thread hole is nice and clean with no paint or smuts on it... same check for the antenna itself...
If all is clean then you need to have them check the underside of the antenna base (above the headlining) as something (screw, plug, etc) may be loose