A closed sketch profile with the right mouse button in display window (radial menu) will be selected . Than you can create an extrude and Edit the closed sketch-profile. If you delete one curve element than Extrude fails to update.
Solution NX infers Selection Intent "Region Boundary Curve (RBC)" rule for internal sketch and object-action scenario. This SI rule creates close regions/loops (if present) from sketch and add them to section discarding open loops. Since this SI rule works only with close profile, it fails to update when region becomes open and this designed behavior of "Region Boundary Curve" SI rule.
Though this is default behavior where "Region Boundary Curve" SI rule is created for object-action scenario, user can change it to create "Feature Curves" SI rule by changing customer default by turning ON toggle "Feature Curves" available at File->Utilities->Customer Defaults->Modeling->General->Miscellaneous Tab-> Toggle group "Selection Intent Rule to Infer Section from Sketch". After this setting, section builder will be created with "Feature Curves" SI rule in object-action scenario and it will fail for given scenario.
Hardware/Software Configuration Platform: all
OS Version: n/a