FDR

Dear R users,

I am wondering about the following results:

p.adjust(c(0.05,0.05,0.05),"fdr")

[1] 0.05 0.05 0.05

p.adjust(c(0.05,0.04,0.03),"fdr")

[1] 0.05 0.05 0.05

Why does p.adjust(..., "fdr") not adjust p-values, if they are constant? 
Does somebody have an explanation or can point to a reference?

Thanks in advance,

Will