AT&T prefix flapping?

[Jonathan Park]

Hi all,
For the past two months, 
it seems that AS7132 (SBIS-AT&T) announces and withdraws about 1,500 prefixes 
to AS7018 (AT&T) monitor every ~80 seconds.  This observation is based on 
AT&T's monitor peering with RouteViews and RIPE.
Does anyone know what's going on?
Thanks,
Jonathan                                          
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