In version 08.11.11.297 of PowerProStructures when you need to Attach Position Flag to a Single Part this version does not let you do it.
1.To attach a position flag to a single part you need to turn on the Subpart Grip.
2. The Subpart Grip symbol will appear green it is coloured triangular in shape.
3. Click on the Attach Position Flag to a Single Part Icon and then select the Subpart Grip.
Note: See video below