Words appearing in text box doesn't keep up with typing speed.

[ProbablyIdiot]

Hello,
I've tried this without a theme applied, and with a different theme, and this is the only one that it happens with. When I try to type into a text box, it is extremely laggy, and doesn't keep up with my typing speed. This is even worse when trying to backspace, as you can hold the button down, and it will do nothing until you release it, when all the text will disappear at once.