Direct Path INSERT requires exclucive lock

There is a table, where we insert rows using serial direct-path INSERT [INSERT /*+ APPEND */].
The INSERT command is executed periodically by a job.
Manually, I run a DELETE command on this table to purge rows no longer needed.
At some point, the job mentioned executes the direct-path INSERT and it gets blocked by the DELETE command with an "enq: TM - contention" lock.

INST_ID	SID	ID1	ID2	LMODE	BLOCK	REQUEST	OBJECT_NAME	LOCK_TYPE	PROGRAM
2	8016	760488	0	3	1	0	AUD$_BU_IDX2	DML	sqlplus@ecdb2 (TNS V1-V3)
2	--->8296	760488	0	0	0	6		DML	oracle@ecdb2 (J001)

According to Oracle Database Administrator's Guide 10g Release 2 (10.2), this is normal behavior:

    During direct-path INSERT, the database obtains exclusive locks on the table (or on all partitions of a partitioned table). As a result, users cannot perform any concurrent insert, update, or delete operations on the table, and concurrent index creation and build operations are not permitted. Concurrent queries, however, are supported, but the query will return only the information before the insert operation.