why ISE par does not tell me all buffer usage?

Hi, I have a V2P7 design going through ISE 6.1, in checking out the PAR report, it tells me in the device utilization section of this,

Number of BUFGMUXs 8 out of 16 50%

But go to timing report table,

+-------------------------+----------+------+------+------------+-------------+

| Clock Net | Resource |Locked|Fanout|Net Skew(ns)|Max Delay(ns)|

+-------------------------+----------+------+------+------------+-------------+

|opb_bram_if_cntlr_1_port | | | | | | | _BRAM_Clk | BUFGMUX4S| No | 2300 | 0.626 |

1.763 | +-------------------------+----------+------+------+------------+-------------+

| MHz33 | BUFGMUX5P| No | 560 | 0.168 |

1.310 | +-------------------------+----------+------+------+------------+-------------+

| ddr_clk_90 | BUFGMUX2P| No | 166 | 0.059 |

1.307 | +-------------------------+----------+------+------+------------+-------------+

| clk_90 | BUFGMUX1P| No | 12 | 0.048 |

1.298 | +-------------------------+----------+------+------+------------+-------------+

| ppc_clk_s | BUFGMUX6S| No | 2 | 0.000 |

1.784 | +-------------------------+----------+------+------+------------+-------------+

| JTGC405TCK | Local | | 1 | 0.000 |

2.514 | +-------------------------+----------+------+------+------------+-------------+

you can see that only 5 BUFGMUX are report here. I wonder where are the other 3 BUFGMUX consumed? Could you give me some clue?

Thanks.