Is there a way to control the way that the ends of lines are drawn? I'm
referring to lines added by hand from the toolbox, not to plotted data lines,
though the same question might apply to data lines.

Sometimes, and perhaps always, the ends are rounded rather than butted at a
right angle. This is particularly apparent when the line thickness is very
large. Each end type might be useful in some situations, but neither is
useful in all cases.

Quick follow-up: I'm told that apparently the 16-bit version draws the same
lines in the same project with square rather than rounded ends. This doesn't
solve the problem, though!