Non-melting chocolate

Parents came up to visit before they headed home as there was a food festival as part of Grad week in the quad. There were some cute little stalls and I always find it quite impressive, that despite the East Neuk's size there is still a lot of great local products. Headed to Balgove to pick up a few bits and pieces for lunch just as the rain started coming down as if it hadn't rained in months.
After parents left we had a lazy afternoon and put a film on before quick gym session before tea.
Had bought some strawberries at Balgove and decided to melt some chocolate to dip them into. Turns out Cadbury chocolate no longer seems to melt and instead becomes solid again...very odd - anyone else discovered this?!