Integration over a subset of meshL

General Discussion
1 
load "msh3"
int nx = 10;
meshL ThLarge = segment(nx,[2*x,0.,0.],removeduplicate=true);
meshL Th = trunc(ThLarge,x<1,cleanmesh=true);

fespace Vh(ThLarge, P2);

varf testvarf(cf,testcf) = int1d(Th)(testcf); 
real[int] rhs = testvarf(0,Vh);

The above code gives me the error message:

current line = 9
Assertion fail : (0)
line :8156, in file problem.cpp

For me it seems that it is currently not allowed to integrate only over a subset (Th) of a function defined on a larger meshL (ThLarge). Is this a bug/not implemented or do I make a mistake?