Random plant event: six-petaled Streptocarpus 'Purple Martin'

Normally, Streptocarpus have flowers with five petals (as well as other gesneriads, like Saintpaulia), which are partly fused into a tube (not true of most Saintpaulias, though semi-tubular Saintpaulias do exist). This particular specimen lost count at some point and wound up with six. It wasn't the only flower on this plant that did this, but there weren't very many sixes before it reverted to fives. (I know it was the same plant because, naturally, I wound up buying it and bringing it home.)

I don't know that this really means anything much, but I'm curious about what would have made this happen, and especially what could have made it happen that would be easily reversible, as this obviously was. [shrug]