Sentence:  If the developer knows the bug is an <WSD>upstream</WSD> bug but does not know which bug it is in the <WSD>upstream</WSD> bug tracker, he can add an <WSD>"upstream</WSD> task" to the bug report. 
Meaning of the word marked with <WSD> tags:  maintained, owned or associated with the original developers of the given software; in contrast to a modified version downstream