The display width does not constrain the range of values that can be stored in the column. Nor does it prevent values wider than the column display width from being displayed correctly. For example, a column specified as SMALLINT(3) has the usual SMALLINT range of -32768 to 32767, and values outside the range permitted by three digits are displayed in full using more than three digits.
update floattest set val=0.05;
update floattest set val=val+10000;
update floattest set val=val-10000;
-- всё штатные транзакции не так ли?
select val from floattest ;
=> 0.0499999999992724
Забыли о кодировании 8b/10b. 300мбайт/с теоретический предел