[BioC] weired bayseq results

[Fatemehsadat Seyednasrollah]

Dear list,

I have used BaySeq to my RNA-Seq data to extract DE genes and I have several biological replicates for each condition(20 replicates for each condition). The point is that if I rerun the BaySeq over my dataset then the number of detected genes with a specific common FDR will change. Can it be possible?
For 10 times rerunning the script the number of detected genes with FDR < 0.05 are :
82, 85, 84, 87, 85, 85, 84, 86, 82, 83

> sessionInfo()
R version 2.15.1 (2012-06-22)
Platform: x86_64-redhat-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=C                 LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] baySeq_1.12.0

loaded via a namespace (and not attached):
[1] tools_2.15.1

Thank you in advance