The following code:

type Foo{K}
end

Foo(K::Type) = Foo{K}()

immutable B{T}
    p::T
end

function run_this{K}(foo::Foo{K})
    # deepcopy(foo)
    result = map(i -> deepcopy(foo), 1:2)
end

run_this(Foo(B))

gives an error:

ERROR: TypeError: _collect: in typeassert, expected Foo{B}, got Foo{B}
in _collect(::UnitRange{Int64}, ::Base.Generator{UnitRange{Int64},##1#2{Foo{B}}}, ::Base.EltypeUnknown, ::Base.HasShape) at ./array.jl:379
in run_this(::Foo{B}) at ./REPL[4]:3

Reproducible on Julia 0.5.0 as well as today's nightly build, though not on Julia 0.4.7.

Any of the following actions remove the error:

• unwrapping code from a function
• uncommenting line deepcopy(foo) (all further calls to map(...) start working too)
• adding type parameter to B in the last line, e.g. run_this(Foo(B{Int}))