This is really nothing new, although always annoying when you are on the receiving end of a transmuter massacre. You will always be at a disadvantage when the person hunting you decides when he is ready to attack, and only under favorable conditions.

You have some counters available to you though.

1) The twitchy edge cannot be underestimated for giving you a warning when something isn't right in an area. I would try learning it and seeing if it gives you a head's up when somebody is nearby that you can't see.

2) There is save vs. para gear you can get around this level range, stuff that isn't terribly hard to farm and keep in your inventory. If you suspect trouble, switch into it and just level a little slower until you are sure you are safe.

3) There's soooo many areas in this game to learn in. A duo transmuter has the advantage since he can just go flat and teleport around the world until he finds somebody vulnerable, but there are also a lot of places you can go where he probably won't want to walk to if he can't randomly teleport until he finds you. Stay out of the known ranking spots and go off the beaten path.

4) Set traps of your own. If a transmuter is harassing you, have friends ready to come to your aid or maybe even help to kill him. Use special terrains or assisting mobs to give you an advantage, too. There's no need to fight fair against somebody who isn't fighting fair with you.