DE2 push buttons question

I made more experiments and I feel that there is problem with buttons edge detection on the DE2 board. I tried T flip flop:

library ieee;
use ieee.std_logic_1164.all;
entity t_ff_async is
   port (
      t : in std_logic;
      r : in std_logic;
      q : out std_logic;
      n_q : out std_logic
   );
end t_ff_async;
architecture struct of t_ff_async is
begin
   process (r, t)
      variable ff : std_logic;
   begin
      -- reset
      if r = '1' then
         ff := '0';
      elsif t'event and t = '1' then
         ff := not ff;
      end if;
      q <= ff;
      n_q <= not ff;
   end process;
end struct;

Toggle is 't' in here - in which I have tested step by step all 4 keys (buttons) on the DE2. Code defines rising edge which is every release of the key (button). I assigned LEDs to Q and n_Q, so LED light should switch with every release of the key (button) which was not 100% event; it sometimes switched also when the button was pressed and then when released. I have also assigned another LEDs to indicate immediate value of the key ledr <= key which is working 100% correct.

So I have reached a view that those type of buttons isn't good to use in applications where edge detection (due electrical characteristic) is needed. Do you think that this could be correct explanation ?

Thanks for reply.