I found the stone rose in Malistaire's lair (i got the message that i found the tenth stone rose), but in my quests it says i still need it.
Has this happened to anyone else?
Are you sure that you still need his stone rose?
There are "two" stone roses in Dragonspyre.
Open your quest log and see which one is still showing in your log file.
One is "Dragonspyre - in the Dragon's Roost". Go to Dragonspyre Academy and ride your battle dragon at Dragon Claw Ridge. As soon as you get off of the dragon, go into the large Circle Room with the Spirit Guardians (I think that was their name). You will see a "low wall" just to the left of the Spirit Guardians. Go around that wall, to the end of it, and the stone rose is in that little corner.
And one is "Dragonspyre - in the Crown of Fire". This one is in the room with Malistaire. Sounds like you already picked this one up, and you still need the one in Dragon's Roost.
Heaven help you on that one. I had that exact same quest bug on me during my pyromancers travels through DS. It took KI almost 3 weeks to do a simple quest update for me. I really hope you have better luck than I did.