Wrong n. of rows in MAL plan?

Could you give me a feedback on whether this is a possible bug or not?

In the following excerpt:

X_377=<tmp_2516>[9]:bat[:str] := mat.packIncrement(X_376=<tmp_2516>[9]:bat[:str],X_335=<tmp_20775>[0]:bat[:str]);"] ... ... X_100=<tmp_2516>[10]:bat[:str] := mat.packIncrement(X_377=<tmp_2516>[10]:bat[:str],X_336=<tmp_24175>[1]:bat[:str]);"]

X_377 has 9 rows. But when it's used as a parameter for X_100, it is reported to have 10 rows.

In between the two instructions above, X_377 is never used.

Roberto