[R] problems with ifelse??

[mousy0815]

I have the following code to determine the probability of a t-cell
encountering an antigen after "m" steps. 

probability <- function(N, f, m, b, x, t) { #using ifelse instead of if/else
	#N is the number of lymph nodes
	#f is the fraction of Dendritic cells (in the correct node) that have the
antigen
	#m is the number of time steps
	#b is the starting position (somewhere in the node or somewhere in the gap
between nodes. It is a number between 1 and (x+t))
	#x is the number of time steps it takes to traverse the gap
	#t is the number of time steps it takes to traverse a node. 
	A <- 1/N
	B <- 1-A
	C <- 1-f
	D <- (((m+b-1)%%(x+t))+1)
	
	ifelse(b<=t, ########starts inside node
			ifelse( (m<=(t-b)),
					return(B + A*(C^m)), # start & end in first node
					ifelse (D<=t,  # we finish in a node
							return((B + A*(C^(t-b)))*((B + A*(C^t))^(floor(m/(x+t))-1))*(B +
A*(C^D))),
							probability(N, f, (m-1), b, x, t)
						)
				),
			ifelse( ########starts outside node
				m<=(x+t-b), 
				return(1), #also end in the gap,
				ifelse (
					(D<=t), #end in a node
					(return(((B + A*(C^t))^(floor((m/(x+t)))))*(B + (A*(C^D))))),
					probability(N, f, (m-1), b, x, t)#outside node
					)
				)	 
			)	
	} 

But I do:
>m<- c(1:3)
>probability(10, 0.1, m, 3, 4, 5)
 0.9900000 0.9810000 0.9729000

but if you do each number separately you get 
>probability(10, 0.1, 1, 3, 4, 5)
0.99
>probability(10, 0.1, 2, 3, 4, 5)
0.981
>probability(10, 0.1, 3, 3, 4, 5)
0.981

Can someone tell me why this is happening??

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