Will the rand() function ALWAYS produce the same result with the same seed?

I am trying to implement a set of encode and decode steganography functions in C, where i use rand() to randomly scatter my data along an array.

I use rand to calculate a random index like so:

unsigned int getRandIndex(int size) {
  return ((unsigned)(rand() * 8)) % size;
}

I seed rand like so:

unsigned long seed = time(NULL);
srand(seed);

I include the seed along with my data as a part of a header that contains a checksum and length.

The problem i have is that while decoding, when i seed the rand function again with the seed i decoded from the data, rand() tends to produce the slightest variations like so:

Index at encode:                  | Index at decode:
---------------------------------------------------------------------
.
.
.
At:                        142568 | At:                        142568
At:                        155560 | At:                        155552
                               --                                  --
At:                        168184 | At:                        168184
.
.
.

Messing up my decoded data.

Is this a limitation of the rand() function? I am 100% sure that the seed is being decoded correctly bit-for-bit as i have verified that.