Thank you Aylinis for the reference to an official word on the subject. They also mention that they clarify things in the next FAQ, which is good to hear.
Thanks. Good to know this will be covered in the FAQ. Here is the wording for Vine Marker from the published PDF of the DvN rules and codex.
Vine Markers (Game Marker)
Vine markers are a Living conjuration with 1
life, no armor, and they cannot gain armor.
Vine markers hinder enemy non-Flying
creatures. Any amount of damage will destroy
a Vine Marker, regardless of its total life.
They can’t be targeted by ranged attacks. Any
number of Vine markers can occupy a zone.
As the Druid, or any object she controls, casts a
vine spell, you can destroy a target Vine marker
she controls as an additional cost to cast that spell. If you do, you
may target that Vine marker’s zone, an object in that Vine marker’s
zone, or a border of that Vine marker’s zone, ignoring range.
If two or more Druids are playing, each should use a different side
of the Vine marker to distinguish ownership.