Something similar happened to me about a year ago. The guitarist, singer and drummer, from the old band were asked to form another band by a bassist they all new. The band is identical to the old band, other than the bassist and an added sax player. The original idea, I was told, is that they were going to be a rockabilly band but as far as I can see they play exactly the same set list as the old band.
The weird thing is, the old band is still gigging with me playing bass and both bands play the same venues, sometimes on the same weekend. So you've got two bands, with virtually the same members, playing exactly the same set, at the same venues. I do wonder why the managers, at the venues that both bands play, haven't figured out that it's the same band, just without me.