Here is what happened :

A table was mistakenly specified to have 2K next rather than 2M.
I started a data load and got ORA-01631-Max extents reached.
Checked the things and changed the NEXT to 2M. Successfully.
Truncated the table and restarted the data load only to get the ORA-01631 error again !!
Checked the NEXT for the table and it was back to 2K !!

When I tested it (806/817), I noticed that when the table is occupying extents equal to MAXEXTENTS value and you change its NEXT and issue a TRUNCATE statement, the NEXT gets the old value again !! TRUNCATE doesn't do anything to NEXT value if the table is NOT occupying MAXEXTENTS extents.

Checked on MetaLink and there is something related to this there (Bug#1546221).

Accepted that this is a documented "feature" (as mentioned in the MetaLink note), but why in the world should TRUNCATE touch the storage values of a table ?