I have this problem resolved now and it will be in the next sub-release.
For those who have full source and would like to try a quick patch, try
this:

IB_Components.pas around line 32429

procedure TIB_BDataset.SysCancelInsertedRow;
begin
Fields.CancelBuffers; // add this line
BufferFields.CancelBuffers; // add this line
SysAdjustCurrentRow( true, true );
end;

Please let me know if this works or not.
My permanent change is a little more involved.

Jason Wharton
www.ibobjects.com