Just started happening to us as well on our newest computer - if I understand the issue. These are solid lines (not dashed) that have the line visually stop before the control end points (about 10% of total line length away from end). If I open a new file and draw a line the problem clears up in the new, but stays in the old. Restarting, etc, to no avail.
Power Mac
Quad Core
10.4.9
VW 12.5