They represent 'temporary' expressions which should really have been deleted. When I see these I write PR's and they generally get fixed so that they are no longer seen. So if you can reproduce these cases, please contact GTAC and have them open a PR since this is not a desired behavior.
John R. Baker, P.E.
Product 'Evangelist'
NX Design
Siemens PLM Software Inc.
Cypress, CA
I have seen that, happens when creating points and a particular option is chosen (associative something, selection dependant I think). I don't have time to try and reproduce it now though.