ALTER TABLE crashes the server

[abmusse]

The alter table command fails and crashed the server.

alter table testtable add column field3 dec(3,0);                 
ERROR 2013 (HY000): Lost connection to MySQL server during query

alter table testtable modify column field2 dec(5,0);            
ERROR 2013 (HY000): Lost connection to MySQL server during query

alter table testtable drop column field2;                          
ERROR 2013 (HY000): Lost connection to MySQL server during query