Valve has still not fixed this yet, theres a bug somewhere that causes that.
I've been making sprays for other members and been telling them to do what Groo said, you must use another source game to convert them. Theres a program out there that does it as well (forgot what it was) that will convert your pic or Targa file to .vtm and .vtf, can some1 care to tell me i always forget.