O.k. man, Here is what you have to do whenever you use tape.
It is sort of a trick that I use, even when I paint rooms in a house.
First make sure the surface of the area that is being painted is clean from oil, dust, dirt, etc. etc., because it prevents the tape from adhereing properly.
Next, apply the tape, without stretching the tape, and use your finger to press the tape securely all along the surface.
Then, from 10 inches away, spray a quick and VERY light coat across the edges of the tape, and let it dry for at least 10 mins, and then continue spraying the rest of the case in thin coats, and allow a couple hours drying time, in between coats.
What you want to do is seal the edges of the tape by using the paint itself, to do so. Thus, preventing the bleeding from happening. Bleeding, is when the paint is applied on too thick and absorbing into the tape and then loosens the seal between the tape and the surface.
But, I will caution you that sometimes (not always) when you use this method the seal is so good, that when you pull off the tape after, it wants to take some of the paint, with it.
So, another solution I use to prevent that is, when applying the paint, using several THIN coats, over and over, about 20 mins in between coats for drying, then when you have a good finish, you remove the tape, and then let it dry over night.
I know it sounds confusing but, good painting comes with experience and the know how, and by using good products, and not mixing laquer with acrylic etc. etc.
The more you do it the better you get at it, and you use what works for you.