the superglue actually heats up when it begins to cure, that is why its important to put the frag back in the water quickly and in good flow.
i like to do the "spot weld", or just the smallest ammount of glue so the frag doesnt fall off, and then immediately in the tank, regardless of how many frags i have out. the glue is much more detrimental that any length of time exposed to air.
but yes, it will overgrow the glue, it will just take a while