Anecdotally, the impression I get is that this happens from time to time in many Paphs, but it seems that it happens more frequently with various clones of P. philippinense and its hybrids. There are some clones where this is apparently a stable trait, so every flower does this every time the plant blooms, but usually it's a bit more ephemeral.
In slipper orchids, the two lower / lateral sepals (which are the petals that form the outer part of the bud) are fused into one synsepal. In most other orchids, there are 3 distinct sepals. For whatever reason, whether it's genetic or environmental (or a little of both) in cause, a developmental issue happens that causes the slipper's sepals to revert back to being split like this.
I think it looks neat. But I suppose it's down to personal preference with these sorts of cosmetic anomalies.