TPL Dataflow block never completes on PropagateCompletion

Question

Since the last alteration to my propagated-completion pipeline, one of my buffer blocks never completes. Let me summarize what was working and what isn't anymore:

Previously working:

A.LinkTo(B, PropagateCompletion);
B.LinkTo(C, PropagateCompletion);
C.LinkTo(D, PropagateCompletion);
D.Receive();

// everything completes

No longer working:

A.LinkTo(B, PropagateCompletion);
C.LinkTo(D, PropagateCompletion);

await A.Completion;
someWriteOnceBlock.Post(B.Count);
// B.Complete(); commented on purpose
B.LinkTo(C, PropagateCompletion);

D.Receive();

// Only A reaches completion
// B remains in 'waiting for activation'
// C executes but obviously never completes since B doesn't either

If I uncomment the commented line, everything works, but obviously that line should not be necessary.

Somehow my BufferBlock B never reaches completion, even though the block linked to it is completed and propagates its completion, and the block linked from it receives all the buffered items.

Answer 1

By awaiting the completion of A none of the remaining code is executed until A completes. That's how await works - the code after it is wrapped in a continuation ready for the completion of the awaited code. So in this scenario B is linked to A after A completes so completion is not propagated I think.