Is it safe or normal for a cyst to fill with blood during ovulation?

Safe and normal: A corpus luteum is the cyst left behind after you ovulate - it often contains blood - a 'hemorrhagic corpus luteum". These cysts are benign, and don't need surgery as they go away on their own. It's a normal thing to see after ovulation. Another kind of blood-filled cyst is an endometrioma, a cyst associated with endometriosis - these cysts may need surgery.

Corpus luteum cyst: After ovulation a structure forms called the corpus luteum. On occasion, the corpus luteum fills with fluid and becomes a "cyst". If the cyst fills with blood, it's called a hemorrhagic corpus luteum, and these are not uncommon. Rarely they can persist, rupture, twist on their blood supply, or cause other problems, but they typically resolve by the time menstruation occurs.