This is called memory. With thin string like throwline you have to put in memory by loading it before you pack it otherwise it will tangle. Do this as Matt describes before climbing and it will cure your tangle problem. If you leave the line in the bag for 24hrs you will probably have to put memory into it again. It depends on the type of line you are using.
Some people coat their throwline with anti static spray as well.
Most use Hot shot braeth freshener, cinamon flavour is best. Take your slickline and tie it to something and hold the other with a object ,to relieve the stress on your hand, and pull with all your might to stretch the crap out of it. It will grow quite a few feet doing this. All ropes retain energy when you load them. This is called memory.