Emacs VHDL mode smart tabs - emacs

Question

I am using VHDL mode in Emacs, primarily for the source code formatting. However, the smart tabs feature shows unexpected behaviour; it inserts tabs for alignment.
The emacs config file: (the two lines at the end are added according to https://www.emacswiki.org/emacs/SmartTabs#VHDL)
(require 'package)
(add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/"))
(package-initialize)
(custom-set-variables
'(package-selected-packages (quote (smart-tabs-mode evil)))
'(vhdl-basic-offset 4)
'(vhdl-indent-tabs-mode t)
'(vhdl-standard (quote (8 nil))))
(custom-set-faces
)
(require 'evil)
(evil-mode 1)
(smart-tabs-advice vhdl-indent-line vhdl-basic-offset)
(setq vhdl-indent-tabs-mode t)
The formatted output: (note that stackoverflow converts the tabs to spaces and note how the ":" are unaligned because stackoverflow apparently uses a tabwidth of 4)
library ieee;
use ieee.numeric_std.all;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity test is
port (
clk : in std_logic;
rst : in std_logic;
verylongsignalname : buffer std_logic;
s : buffer std_logic);
end entity test;
Running the vhdl-beautify-buffer in batch mode with -Q leads to the same result.
How do I prevent it from using tabs from alignment, while still using tabs for indentation?