MySQL Create Table as SELECT

Everytime I use MySQL's CREATE TABLE AS SELECT ... all the tables/indexes being selected from are locked for the duration of the query. I do not really understand why? Is there any way around this?

Using: MySQL 5.1.41 and InnoDB

Added Example:

For example, the following query might take up to 10 minutes to complete:

CREATE TABLE temp_lots_of_data_xxx AS 
SELECT
    a.*
    b.*
    c.*
FROM a
LEFT JOIN b ON a.foo = b.foo
LEFT JOIN c ON a.foo = c.foo

Trying to update values in tables a, b or c during the above query will wait for the above query to finish first. I want to avoid this lock, as I am not interested in the most complete data in the created temp table.

p.s. SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED; yields no change in behavior.