On August 2, 1985, Bulgaria issued four stamps commemorating the 1985 European Aquatics Championship in Sofia. One of the stamps (60 Stotinki face value) featured a synchronised swimmer with a respective routine. Since the stamp's text and face value were printed inversely, the routine did not comply with gravitational conditions since the swimmer was above the water surface instead of below. A corrected stamp was issued.

Left: Inverted text stamp

Right: Corrected stamp

Stamps not affected