Drawing artifact with powerline tab bar and @ set-colors #3595

$ kitty --debug-config
kitty 0.20.3 (c891432c9d) created by Kovid Goyal
Linux byteevo-scm 5.8.0-50-generic #56~20.04.1-Ubuntu SMP Mon Apr 12 21:46:35 UTC 2021 x86_64
Ubuntu 20.04.2 LTS \n \l
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=20.04
DISTRIB_CODENAME=focal
DISTRIB_DESCRIPTION="Ubuntu 20.04.2 LTS"
Loaded config files: /home/precor/.config/kitty/kitty.conf
Running under: X11

Config options different from defaults:
active_tab_font_style         (True, False)
adjust_line_height            1
enabled_layouts               ['splits', 'fat', 'grid', 'horizontal', 'stack', 'tall', 'vertical']
font_family                   Hack
initial_window_height         (32, 'cells')
initial_window_width          (128, 'cells')
placement_strategy            top-left
remember_window_size          False
scrollback_pager              ['vim', '-R', '+AnsiEsc', '+au VimEnter * noremap q :q<CR>', '+setlocal buftype=nofile', '+normal INPUT_LINE_NUMBERzt', '-']
scrollback_pager_history_size 16777216
tab_bar_edge                  1
tab_bar_style                 powerline
window_padding_width          FloatEdges(left=1.0, top=10.0, right=1.0, bottom=0)
Added shortcuts:
	f1 KeyAction(func='toggle_marker', args=['regex', ((1, '\\bERROR:?'), (2, '\\bWARNING:?'), (3, '^FAILED')), re.IGNORECASE|re.UNICODE])
	ctrl+l KeyAction(func='combine', args=(KeyAction(func='clear_terminal', args=['scrollback', True]), KeyAction(func='send_text', args=['normal,application', b'\x0c'])))
	ctrl+tab KeyAction(func='next_window', args=())
	ctrl+page_up KeyAction(func='previous_tab', args=())
	ctrl+page_down KeyAction(func='next_tab', args=())
	shift+ctrl+\ KeyAction(func='combine', args=(KeyAction(func='new_window', args=()), KeyAction(func='new_window', args=()), KeyAction(func='goto_layout', args=['tall']), KeyAction(func='resize_window', args=['shorter', 12])))
	shift+ctrl+tab KeyAction(func='previous_window', args=())
	alt+ctrl+d KeyAction(func='launch', args=['--location=hsplit', '--cwd=current'])
	alt+ctrl+r KeyAction(func='launch', args=['--location=vsplit', '--cwd=current'])
Changed shortcuts:
	shift+ctrl+t KeyAction(func='launch', args=['--type=tab', '--cwd=current'])
	shift+ctrl+enter KeyAction(func='new_window_with_cwd', args=())