[AHB eVC]Unexpected 1ps delay on BFM

Hi, 

Another question on AHB eVC.

For some reason, when the master agent drives the AHB signals (to be specific, HSIZE and HADDR), sometimes there will be a 1ps delay(clock period is 3.75ns).

It may or may not happen depend on the seed used. So confused and by checking the log, I dont see any unexpected delay. The logger said that bfm drives the signal at the rising edge of the clock exactly.

Have anybody encountered the same problem? 

Any help or your best guess will be appreciated.

Thanks a lot.