in src/lib/vterm.cpp

    if (mode_flags.insert_mode) {
            changed_line(cursor_y, cursor_x, width - 1);

            u16 step = dw ? 2 : 1;

if 0

            for (u16 i = cursor_x; i < width - step; i++) {
                    text[yp + i + step] = text[yp + i];
                    attrs[yp + i + step] = attrs[yp + i];
            }

else

            /* BUG FIXED */
            for (s32 i = width - step; i >= cursor_x; i--) {
                    text[yp + i + step] = text[yp + i];
                    attrs[yp + i + step] = attrs[yp + i];
            }

endif

    } else {
            changed_line(cursor_y, cursor_x, cursor_x + (dw ? 1 : 0));
    }

Thanks for your patch, but the loop start index should be (width - step -1)