Thanks for this useful plugin! I installed it today and it mostly seems to work well. I've encountered two problems, however.
One problem I see is that the "expand" icon used on a sub-category is wrong when the page first loads. It shows - when it should be +, and the same problem occurs when using the triangle option. After expanding and contracting the sub-categories the icon is correct.
You can see this at girlwithaglass.com/blog. The category list is in the left column. Click on the + next to For Wine Drinkers. You'll see that the symbol next to the sub-category Learn About Wine is - when it should be +. I see this in Chrome and Safari on Mac.
The other problem occurs when using Safari on Mac. I've set ex_sym=+ and con_sym=- in my shortcode, yet once the + icon is clicked, it changes to a triangle and remains that way!