Custos incorrect before clef change at line break #1750

As noted in gregorio-project/gregorio-test#415, the test clef_change.gabc has a misplaced custos at the end of the first line:

Given the shift from the do clef to the fa clef shouldn't the custos at the end of line 1 be either on the top line or the space just below the lines? The note in syllable test5 (at position g) is a mi in the new key, but the note in syllable test4 (also at position g) is a ta.