QSpinBox in QTableWidget valueChanged not firing

This bug presents when I put a whole lot of QSpinBox's inside a QTableWidget. When you run the attached example, the message "Row.print_str called" is displayed when the valueChanged event fires on rows 1 to 5 (and oddly row 10) of the table, but on rows 6 to 9, the valueChanged event doesn't fire and nothing is printed. The only difference between the QSpinBox's that work and don't is whether they are saved in a list after creation or not. So it seems like this is a garbage collection or reference counting problem, where the spinboxes that are not stored in a list are getting disposed of prematurely. See the following lines:

# these are saved in a list
# and so seem to work
rows = []
for x in range(0, 5):
    row = Row(t, x)
    row.add_to_table()
    rows.append(row)

1. these rows don't work
   # presumably due to a garbage
   # collection/reference counting bug
   for x in range(5, 10):
       row = Row(t, x)
       row.add_to_table()

Note: I'm using PySide._version_ 1.2.4 but this doesn't seem to be an option in the affects version dropdown.