Why does the line tool not stay active after I draw one line?

I'm not clicking the end of the line, I'm clicking to end the line as in:

I click once (origin), then click somewhere else, a line is created, but the line tool ends and doesn't let me continue drawing the line.

For example:

I want to draw a triangle.

I use the line tool.

I click point 1 and then I click point 2 (some distance away horizontally). The line tool is supposed to continue to allow me to finish drawing the triangle without me having to re-activate the line tool.

If I click and drag from point 1 to point 2, then it does this correctly by drawing a line, but the tool closes again.

In either case, the tool should stay open.

it is unchecked.

thanks for looking though.