Just found this issue in the common bugs section. Please ignore.
After activating a piece of spinach for the enhanced movement effects, I activated a signpost to travel along a different street. I then experienced the occasional "you have been disconnected from server..." notice. About a minute or later I realized that the effect wasn't wearing off, and the effect seems to be permanent either for this session or until the next game day. I'm not 100% sure that the server disconnection was the source of the problem, but it's the most likely culprit considering the small time frame that the spinach effect normally uses.