Visual artifact in wibar tasklist with custom template

[jcrd]

Output of awesome --version:

awesome devel (Too long)
 • Compiled against Lua 5.1.4 (running with LuaJIT 2.1.0-beta3)
 • API level: 4
 • D-Bus support: yes
 • xcb-errors support: no
 • execinfo support: yes
 • xcb-randr version: 1.6
 • LGI version: 0.9.2
 • Transparency enabled: yes
 • Custom search paths: no

How to reproduce the issue:

This is the relevant code:

local function update_tasklist(widget, c)
    local b = widget:get_children_by_id('background')[1]
    if not c.minimized then
        b.fg = beautiful.fg_focus
        b.bg = beautiful.bg_focus
    else
        b.fg = beautiful.fg_normal
        b.bg = beautiful.bg_normal
    end
end

screen.connect_signal('request::desktop_decoration', function(s)
    s.mytasklist = awful.widget.tasklist {
        screen          = s,
        filter              = awful.widget.tasklist.filter.currenttags,
        buttons         = ez.btntable(config.buttons.tasklist),
        widget_template = {
            {
                {
                    {
                        {
                            id = 'icon',
                            widget = wibox.widget.textbox,
                            forced_width = beautiful.font_size + dpi(2),
                        },
                        right = dpi(6),
                        widget = wibox.container.margin,
                    },
                    {
                        id = 'text',
                        widget = wibox.widget.textbox,
                        align = 'center',
                    },
                    layout = wibox.layout.align.horizontal,
                },
                left = dpi(10),
                right = dpi(10),
                widget = wibox.container.margin,
            },
            id = 'background',
            widget = wibox.container.background,
            create_callback = function(self, c)
                local n, i = clients.get_name_and_icon(c)
                i = util.icon_markup(i, 'xx-large', -(beautiful.font_size * 250))

                self:get_children_by_id('text')[1].text = n
                self:get_children_by_id('icon')[1].markup = i

                update_tasklist(self, c)
            end,
            update_callback = update_tasklist,
        },
    }
end)

Note: this is a high DPI environment.

Actual result:

Occasionally, the background container affects only a portion of the text widget.

(The blue bar under the tasklist widget is a client titlebar.)

Expected result:

The background container should affect the entirety of the tasklist widget segment.