The point is that the command

does not yield the MACD signal line, but the so-called MACD signal (in the standard PRT indicator), which is the difference between MACD and the signal line. Someone has mixed up these two while coding them.

But who uses MACD or similar indicators anyway for real trading systems ? In my eyes, they create too many unreliable signals because they can wiggle around far too often and quite heavily. Maybe this is a reason why nobody has reported this bug so far.