plotting a saved file with one IF doesn't work

[G.Fuller@…]

Code to demo bug:

    d = scantable('2010-03-24_1445_316p81-0p06.rpf')

    m = d.auto_quotient()

    m.set_freqframe('LSRK')
    m.set_unit('GHz')
    m.freq_align()

    iffreqs = [23.6945e9,24.13939e9]

    m.set_restfreqs(iffreqs) # Set the (1,1) and (4,4) freFs
    pdq = m.average_pol(weight='tsys')
    av = average_time(pdq,weight='tsys',align=False)
    bsp = av.copy()
    
    bsp.save('blspec',overwrite=True)
    resp=scantable('blspec')
    plotter.plot(resp)

works but

    ifno=0
    sel=selector()	
    sel.set_ifs(ifno)
    bsp.set_selection(sel)

    bsp.save('only1IF',overwrite=True)
    resp=scantable('only1IF')
    plotter.plot(resp)

dies with the message

/usr/lib64/python2.6/site-packages/asap/asapplotter.py in _plot(self, scan)
    765                     y = scan._getspectrum(r, polmodes[scan.getpol(r)])
    766                 else:
--> 767                     y = scan._getspectrum(r)
    768                 m = scan._getmask(r)
    769                 from matplotlib.numerix import logical_not, logical_and

RuntimeError: Table DataManager error: Invalid operation: MSM: no array in row 0 of /local/home/gaf/DATA/Parkes/MMB_NH3/temp14634_856/table.f1