Prior to 10.3, while registering an Oracle Spatial (SDO_GEOMETRY) layer using the SDE command line, if you did not include the option for CAD data in the entity mask, the underlying table was left as-is (no additional columns were added). However, that option was not ported over in 10.3 with the deprecation of the SDE command line, so anytime you register an Oracle Spatial layer in 10.3, regardless of the type of geometry (point, line, area, CAD, etc.) a new field named SE_ANNO_CAD_DATA is automatically added to the underlying table. Adding this field changes the structure of the table unnecessarily and may break any script, application, form, procedure, etc. that relies on that structure to remain as-is.
Please continue to add the SE_ANNO_CAD_DATA field only when the user explicitly chooses the CAD data option.