Oracle released APEX 4.2.6 yesterday, it's also available from My Oracle Support as a patch set 19595896.
Here's the table of bug fixes.
Importing pre-4.2 application with data loading results in runtime error
Corrupted HTML mail messages are created from
Errors picking up session with cookie when
Oracle Application Express 4.2.4 throwing error while generating check boxes
Check box fails with
Applying the patch took less than 7 minutes.
This is probably the latest patch before APEX 5.0 hits the road...