delete property from symbol

Hi

I've made a skill program that uses properties on symbols but have experienced an issue that I cannot solve for the attached symbol.

If I look at Setup->Property definitions it shows NS_REV_100_COMMENT and NS_REVISION_CODE and I can't delete them in that menu or with axlDBDeletePropDictEntry since it is in use.

If I do a Edit->Properties on Drawing it does not show this property as being part of the symbol drawing.

If I inside the Skill window do props = axlDBGetProperties(axlDBGetDesign()) then it will show these 2 properties as being part of the symbol

This should mean that the following code first deletes the usage of the property and then the property definition, but this does not happen.

 propname = "NS_REV_100_COMMENT"
 axlDBDeleteProp(axlDBGetDesign() propname)
 axlDBDeletePropDictEntry(propname)

This works for lots of other symbols but not for this one, anyone with an idea to the issue? 

Best regards

Ole