Hi Glenn,
The conversion from the Numbers 2 format is (obviously) buggy.
I don't know how complicated your table is but here what often works when other methods are messy is to select the table in Number 2.3 (as an object), command-c, click on the canvas in Numbers 3.0, command-v. (Both versions can be open at the same time).
Whether you want continue to use Numbers 2.3 or switch to Numbers 3.0 depends very much on how you use Numbers. If you need to print a lot of complicated documents, you won't be happy. If you want iCloud sync that works well and cross-platform capabilties and other new features, you will be *much* happier. There are workarounds for many of the missing features and some features will beadded back in.
SG