I've hit this bug a few times, but it got me during server wars tonight. Basically on occasion I wont be able to head in a certain direction. Tonight it was north. It's not my mouse because I tried using the laptop touchpad when it happened and the problem was the same. btw I hate pathfinding altogether, can I turn it off?
Pathfinding can be turned off in your options menu. refer to my guide here The not being able to run a certain direction is you unsyncing with the server. This is fixed by using Razor. Go under the "Hot Keys" tab, scroll down to Misc, then find "Resyncronize with server" I'd advise setting a hot key to it, but you can simply click "Execute Selected" in a pinch.
An easy way to fix this problem is to re-open your paperdoll. When I played actively on another server anytime I would recall in somewhere(running) or be running frantically it would cause a de-sync with the server. Basically the server had me in one position, while my client had me in another position. So in reality you are trying to run into a tree, while on your client it looks like a clear path. Razor also has a re-sycn feature you can work into a macro to help with the problem.