we had an issue with the matrix datatype in eZ 4.0.1
if you create a matrix table then the matrix name of the second table is always wrong.
its written "Col_2" instead of the real name. this is because of:
kernel/classes/datatypes/ezmatrix/ezmatrix.php (Line 876)

original(bug):

if( $column != null && $column['identifier'] != 'col_'. $i+1 )

our current(fixed):

if( $column != null && $column['identifier'] != 'col_'. ($i+1) )

patch file attached.

Steps to reproduce

• create new class
• add matrix datatype to that class as attribute
• create at least 2 colums in that matrix datatype and give proper names
• publish that class
• create a new object with your new class
• add some rows to your matrix attribute
  => you will see the wrong 2nd column name