whats going on with the bottom of this stone? Is that normal or just me? From those photos is looks like theres no culet at all just a flat circle- or am I seeing things?
Ametrine,
The angles of the bottom few pavilion facets are cut too shallowly to allow the light (and colour) to bounce back to the eye, hence the colour appears to leak through right through the bottom of the gemstone. In short, yes, that is a small window. That said, the window is so small that I expect it to "close up" or not be noticeable once it is set.
That appears to be a flat culet. In fact, there are some very famous diamonds with 90 degree culets like that. I don't personally like them, but they sometimes have to exist on shallow material.