about transaction(mysql)

[KFC]

I am new to PHP. All my codes of accessing MySQL in hand are from google. I got a queation about transaction. Following a sample from google, I have

  $conn = mysql_pconnect(...);
  query('set autocommit=0;');
  query('start transaction;');
  foo1(); // some sqls updating table1
  foo2(); // some sqls updating table2
  foo3(); // some sqls updating table3
  if (ok) 
    query('commit;');
  else query('rollback');

here, query() is an user-defined function for querying the database with the given sql.

Before the stage of foo3, foo1 and foo2 has already change the table, and in foo3 a piece of code is added for confirmation. The code given above seems ok to me. However, I try to push the 'BACK' button on IE rather than pushing the 'confirmation' in foo3 and it makes mysql down ( I cannot access table1, table2 unless I restart mysqld). I try to repeat the experiment but nothing wrong again. It's confusing me! I WONDER if it will crack the mysql if I start a transaction without correctly closing it by tirggering 'commit' or 'rollback'.

[KFC]

Oh. The problem occurrs again!!! I found that no matter if I am correctly end up a transaction with 'commit' or 'rollback', wheneve I run the following sql likes

update table1 set modi = NOW(),  nb = nb + 1 where id=2;

the probelm happend and down the mysql. I wonder if it is the bug of InnoDB???