Using @ variables with LIKE,CONCAT

[Hank]

This used to work fine in Mysql 4.3, but no longer works in 5.5.8:

set @txt='needle';
select * from table where field  like CONCAT('%',@txt,'%');

--returns the null set.  If I substitute like this:

select * from table where field  like '%needle%';

it works perfectly (and as it did in 4.x).

How can I get this to work in 5.5.x?

Thanks,

-Hank