Delete _new table from pt-online-schema-change
Like many other solutions designed for an almost lockless schema change, pt-online-schema-change works by creating triggers on your table and creating a _new table. As stated in the documentation:


  Any modifications to data in the original tables during the copy will
  be reflected in the new table, because the tool creates triggers on
  the original table to update the corresponding rows in the new table


If this utility crashed, you might have to do the cleanup yourself. This might include:


Removing the triggers: have a look at the SHOW TRIGGERS  syntax to see the ones pt-online-schema-change has just created;
Delete the _new table.