AutoCAD Inventor :: Lines For Sections In Drawings?

This is happening on both 2012 and 2014, the workflow was what I followed offline to try and replicate an issue on a live project: Start a new partDraw a rectangle 10m x 10m fully constrainedExtrude by 10mSaveStart a new .dwg format drawing (though same results if using out of the box .idw)Place a top base view of the partSection the part anyway or direction in such a way not to infer any constraintsSection properties set to include slice and slice the whole partPlace the sectionEdit the sketch of the section lineApply a "fix" constraint to the line itselfFinish the sketch I then get an error saying the sketch does not contain a valid section line and the section disappears
 
he section line sketchRemove the fix constraint from the lineFinish sketch My section then reappears
 
Edit the section line sketchUse a "fix" constraint on each end of the lineFinish the sketch

My section remains. We're experiencing a lot of problems of section lines and therefore sections disappearing even though we're not directly applying fix constraints, I was wandering if Inventor applies a fix constraint should geometry that a section line is constrained to disappears.