local_rdata_valid in DDR2 Controller V7.2 SP3

HI:

i have a problem about the local_rdata_valid in my design，i use DDR and DDR2 SDRAM Controller V7.2 SP3，DDR2 chip is MT47H16M16，and i find the signal local_rdata_valid the controller output sometimes delay one clock output and sometimes output right even the same sof file ，that is this time i downloader once my sof file and the local_rdata_valid output is ok，but next time i downloader the same sof file and the local_rdata_valid signal output delay one clock.i get the signal with signaltap!

can any one tell me why?