What causes this text distortion when uploading an image to facebook?

We recently created a single image with both text and photography, but when we upload the image to facebook the text becomes distorted. We tried uploading at different resolutions but each time the photograph was perfect but the text became distorted.

See the image in question here
https://www.facebook.com/thevelostore/photos/a.246276025411684.56859.245692875469999/1763930920312846/?type=3&theater

Many thanks

Gavin