Naming double bond sidechain In IUPAC naming double bonds take preference over an alkane chain of any length, right? So the above should be named as 2-ethylnon-1-ene.

However, when I verify with chemdraw it gives the answer as 3-methylenedecane. I cannot seem to find any mention of double bond side chains as alkylene anywhere on the internet... Is this common nomenclature, and if not why would chemdraw name it as this?
It looks like you're correct.

This molecule has been given 2-ethyl-1-hexene or 2-ethylhex-1-ene
  

Another name for your molecule would be 3-methylidenedecane. 

Added from Wikipedia:      

The trivial name carbene is the preferred IUPAC name. 

The systematic names methylidene and dihydridocarbon are constructed according to the substitutive and additive nomenclatures, respectively.