In section 3.2, in step 3.1 of the abort method, the spec says:
"Abort the segment parser loop, buffer append , and stream append loop algorithms if they are running."

In section 2.2, in step 3.1 of the removeSourceBuffer method, the spec says:
"Abort the stream append loop algorithm if it is running."

In Section 3.5.3, in Append Error, the spec says:
"Abort the stream append loop algorithm if it is running."

I think these three texts should be aligned. In particular, the "segment parser loop" algorithm can be called only by the "Buffer Append Algorithm" or the "Stream Append Loop". So aborting the buffer append and stream append loop should suffice (in 3.2.3.1). Then, the removeSourceBuffer should also abort an appendBuffer operation (if any).