Hi… @dave62: I can’t say for Blender per se, but it seems to me that the real problem is in the the geometry. It’s a common problem for those who work in wood to make sharp bends in, for instance, a picture frame. The problem is that if you start with a “bevel” (i.e. a “cross=section” in woodworking terms), the shape of the bevel at the joint of the two curves is not the same as the shape along a straight section. In this case you seem to have compounded the problem by starting the bevel out at an angle to the curve (and I have no idea how you did that).
@dalex: You made it even “worse” (compared to your desired result) by having very acute angles, which magnify the distortion. In addition you seem to have added some taper to your curve, since a simple bevel could not reduce the width of the extrusion along a straight path.
Two possible solutions suggest themselves. 1) divide your curve into sections and bevel each section. 2) Don’t make such sharp bends (depends on you desire of course: if you are trying to make a picture frame, well you need the sharp angles.
Just a few thoughts from a Blender noob.