Yep. I've been there also!
For me it also started at about 25m. The first time I got this, I stopped diving immediately for that day. It appeared again soon and now I spit blood every summer for time to time. Not much, but it's blood anyway. I'm not sure if it's coming from my lungs or throat. First it starts to tingle in my throat and then starts couching and spitting little blood, not much but anyway.
I have been talking to many people about this subject and many of them think, that it's something normal and it will not kill you (even though some say that it's very dangerous because it can cause secondary drowning). I've noticed also, that when having hard time to equalize, spitting blood occurs more often.
I heard a theory that the blood is coming through your "alveoli" because of negative pressure in lungs. This is because you are not strech enough. At first I was affraid about this thing, but I kept diving the same way and stretching more often also. Suddenly I noticed, that I can go deeper and deeper and no bleeding. I think my body had adapted to go deeper and diaphragm had became more strech (which is very important).
I think I will spit little blood when going to open water again after winter, but I'm sure it will also stop at some point.
-antti-