Beautiful shape Alan - too bad about "the nubbin'.
A couple of thoughts you might consider............first. if you have a nice sharp scraper, you could try taking the bottom/inside nubbin' off with the the lathe off. Put the scraper under the nubbin and turn the piece by hand. You should be able to whittle it away if the piece you are turning isn't too deep and you won't risk going beyond the center with your tool (while it is powered) which can cause the tool to twist, etc.
Secondly, in the future, when doing your Pewa patches, think about going just beyond what you see as the "end of the crack" and installing a Pewa. In theory, that will stop it from cracking any further. If you don't go just beyond what you can see as the end of the crack, there's a "chance" it will continue to crack, along that same line, especially as the wood expands and contracts. The crack shouldn't "jump across" a Pewa blocking it.