On Thu, 2017-10-12 at 17:55 -0400, Jon LaBadie wrote:
On Thu, Oct 12, 2017 at 10:56:51AM -0700, Jonathan Ryshpan wrote:
In the command interpreter (shell) the underline character (underline_char) generally but not always echos as a space when actually typed and generally but not always displays as an underline when produced by the system. For example: (1) $ echo underline_char (2) underline_char the underline echos as a space when actually typed on line (1) but then changes to an underline when I hit return and line (2) appears. Line (2) displays properly.
My terminal program does not leave any room below the last screen line and the window frame. Underscores typed on the last line are masked by the window frame. Underscores display properly on lines above the last line. I see the same results you do. Line 2 appears normal because the shell prompt bumps line 2 off the last line.

Not the problem here, since the underline_char does not appear even when the screen is cleared (say by CTRL/L) so the line of interest is at the top of the screen.