RadTrackBarElement - has incorrect behavior when AutoSize property is false. If you set value to be equals to Maximum the thumb will be go out of the TrackBar's rectangle.

Workaround:
Turn off auto size and manually set the desired size of the element. For example:

this.radTrackBarElement1.AutoSize = false;
this.radTrackBarElement1.Size = new System.Drawing.Size(100,20);