Grr, forgot to look into a file where I recorded STDERR.


Debug memory block at address p=0x449e6900: API 'o'
    80 bytes originally requested
    The 7 pad bytes at p-7 are not all FORBIDDENBYTE (0xfb):
        at p-7: 0xfb
        at p-6: 0xfb
        at p-5: 0xfa *** OUCH
        at p-4: 0xfb
        at p-3: 0xfb
        at p-2: 0xfb
        at p-1: 0xfb
    Because memory is corrupted at the start, the count of bytes requested
       may be bogus, and checking the trailing pad bytes may segfault.
    The 8 pad bytes at tail=0x449e6950 are FORBIDDENBYTE, as expected.
    The block was made by call #8155854715 to debug malloc/realloc.
    Data at p: 00 00 00 00 00 00 00 00 ... 20 af 5b 3b 0e 7f 00 00
Fatal Python error: bad leading pad byte
Fatal Python error: Aborted

Current thread 0x00007f0e3b7ec700:
  File "/usr/lib64/python2.7/site-packages/matplotlib/axes.py", line 932 in cla
  File "/usr/lib64/python2.7/site-packages/matplotlib/figure.py", line 906 in clf
  File "/usr/lib64/python2.7/site-packages/matplotlib/figure.py", line 926 in clear
  File "blah.py", line 12513 in draw_hist2d_plot

In that function I call:
        del(_series)
        del(_ax1)
        _figure.clear() # 12513