Why does Gremlin idx returns with null although the DB is not empty?

Question

I am opening a graph using:

g = new Neo4jGraph('...path...');

then adding a vertex using:

myVertex = g.addVertex(['type':'X', 'Y':Z]);

I can see the db afterwards has a single vertex (using Gephi) but when I run:

if (g.idx(T.v) != null )

it always returns false. Should the indexing be turned on somehow? Does Gremlin require a specific Neo4j version?

Adding some log info:

...
==>v[22092]
==>v[22093]
==>v[22094]
==>v[22095]
gremlin> g.idx(T.v)
==>null
gremlin> g.idx("vertices")
==>null
gremlin> g.indices
gremlin>

Tried this on Gremlin 1.3 - same results. So I guess it is something I am missing.