Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

This is a limitation in the implementation. For the class constant we need a constant value at compile time and can't evaluate expressions. define() is a regular function, evaluated at run time and can therefore contain any value of any form.

changing this would mean to add an execution phase in the compiler ...

And yet the following works:
define( 'FOO', 'foo' );
define( 'BAR', FOO . 'bar' );

class ThisWorks {
  const bar = BAR;
}

echo ThisWorks::bar;

If class constants are really compile time dependent, why is it ok to set one to 
a global const value which is only evaluated at run time?

In a more complicated example that shows how these dependencies are not clear-cut, 
the following also works:

define( 'BAR', ThisWorks::foo . 'bar' );

class ThisWorks {
  const foo = 'foo';
  const bar = BAR;
}

echo ThisWorks::bar;

this will output 'foobar' without an error.

In your response, you wrote - 
For the class constant we need a constant value at compile time and can't 
evaluate expressions. define() is a regular function, evaluated at run time and 
can therefore contain any value of any form.

However, why then does the code example from 2010-05-07 15:57 UTC work? This has 
a "compile time" class constant populated properly by a define() that is only 
evaluated at run time with a string concatenation. By your definition, this code 
should fail. Yet it doesn't, so I don't see how your explanation actually makes 
sense.