Starting with the following definitions
```julia
abstract Vartype
type VT1<:Vartype
end
abstract Graph{T<:Vartype}
abstract Subgraph{T<:Vartype} <: Graph{T}
type Vertex{T<:Vartype} <: Subgraph{T}
end
type Block{T<:Vartype,N} <: Subgraph{T}
end
abstract GraphObject{T<:Vartype}
type SubgraphObject{T<:Vartype,S<:Subgraph{T}} <: GraphObject{T}
end
typealias VertexObject{T<:Vartype} SubgraphObject{T,Vertex{T}}
typealias BlockObject{T<:Vartype,N} SubgraphObject{T,Block{T,N}}
typealias VertexBlockObject{T<:Vartype}
Union(VertexObject{T},BlockObject{T})
O1=SubgraphObject{VT1,Vertex{VT1}}()
O2=SubgraphObject{VT1,Block{VT1,3}}()
```
I did not expect all of the following to be true, but nevertheless got the
results in the comment
```julia
isa(O1,VertexObject) # false
isa(O1,VertexObject{VT1}) # true
isa(O1,VertexBlockObject) # false
isa(O1,VertexBlockObject{VT1}) # true
isa(O2,BlockObject) # false
isa(O2,BlockObject{VT1}) # false
isa(O2,BlockObject{VT1,3}) # true
isa(O2,VertexBlockObject) # false
isa(O2,VertexBlockObject{VT1}) # false
```
I don't see how this is different to `isa(randn(3,3),StridedMatOrVec)`,
which returns `true` with or without full specification of the argument.
Is this a bug or expected behaviour?
