ddl - TYPO3, looped DB changes while trying to add a key to other table -

I expand in detail of my expansion: (usually, to keep DAM sources unchanged) and a task Tx_dam Adding a field to the table In my ext_tables.sql file I added (small):

  create table Tx_dam (# other field direct_download Tinyint (4) unsigned DEFAULT '0' no, tap, key file_path (file_path));   
 And the DB comparison tool adds new fields as needed and there is no problem in it, but every time I compare the device (or am updating the DB from EM) Drop and want to rebuild  file_path  key, in just one step:  
  optional table tx_dam DROP KEY file_path; Add optional table tx_dam key file_path (file_path);   
 Why is that so? Is it possible to create any kind of bug, or key, only the original  ext_tables.php ?   
 
 
 TYPO3 simply supports a subset of SQL and checks DB against the definition of area of ​​DB Comparison If the refunded string does not match the expected value, then it needs modification.  
 Try removing the location before the bracket.  
 If it does not help, then it is important to know why your database keys provide information.