P. damicornis is a brooder, and an excellent one for research. Yes, your adult colony is releasing planua larvae that are settling out as primary polyps, and they will develop into full-blown adult colonies that can then release their own brooded larvae, etc.
I at one time had P. dam covering the entire back wall of my 120, which looked awesome, but as others have mentioned, they become something of a pain when they settle out right next to that prized ORA "something-or-other" acro that then gets out-competed for space by the P. dam.
To control, you can epoxy or drizzle kalk paste of the recruits to cull them. You can also use Night Sea to help find them after the lights have gone out. You might be very surprised to see how many you actually have... The planua larvae also fluoresce, so you'll see little "flatworms" crawling around that are glowing.
Cheers
Mike