Thanks Luke, although I don't recall ever seeing it before last night.  Maybe just never noticed it...

Now I'm trying to figure out why my all time average and effective average has changed.  I was pretty much 2's across the board until last night, but there were lots of rebuilds on the system yesterday.

bfgminer version 3.10.0 - Started: [2014-02-07 10:15:53] - [  0 days 02:24:
 [M]anage devices [P]ool management [ S]ettings [D]isplay options [H]elp [Q]u
 Connected to us-east.multipool.us diff 64 with stratum as user Cassey.miner
 Block: ...b3a79105 #752072  Diff:7.65k (54.79Gh/s)  Started: [12:40:22]
 ST:8  F:3  NB:43  AS:0  BW:[871/ 10 B/s]  E:2.80  I: 3.54 BTC/hr  BS:9.36k
 6            | 12.73/ 6.46/ 5.37Gh/s | A:319 R:45+6( 14%) HW:8/.06%
----------------------------------------------------------------------------
 AMU 0:       |  2.06/ 1.08/ 0.91Gh/s | A: 50 R: 7+0( 12%) HW:2/.10%
 AMU 1:       |  2.06/ 1.08/ 0.83Gh/s | A: 60 R:11+5( 21%) HW:2/.10%
 AMU 2:       |  2.05/ 1.08/ 0.96Gh/s | A: 59 R: 6+0(9.2%) HW:1/.05%
 AMU 3:       |  2.05/ 1.08/ 0.91Gh/s | A: 54 R: 7+0( 11%) HW:1/.05%
 AMU 4:       |  2.06/ 1.08/ 0.93Gh/s | A: 53 R: 4+1(8.7%) HW:2/.10%
 AMU 5:       |  2.05/ 1.08/ 0.86Gh/s | A: 44 R:10+0( 18%) HW:0/none
----------------------------------------------------------------------------
 [2014-02-07 12:40:18] Accepted 0347e94d AMU 0  pool 0 Diff 78/64
 [2014-02-07 12:40:22] Network difficulty changed to 7.65k (54.79Gh/s)
 [2014-02-07 12:40:22] Stratum from pool 0 detected new block

Maybe its just a reporting change? When I look at the pool stats I see:

Active Workers
      Hashrate
Coin   Worker Name   1 minute   10 minute
btc   Cassey.miner2am   13744   12599

Which is a bit higher than the 12Gh/s I expected, but in line with the 20-second decaying rates reported above.