How can a trigger be bypassed? Assuming I have the following table:

Create Table [dbo].[Test_IP]
(
  [IP] varchar(40),
  [IPType] varchar(6)
)


There are more triggers on this table, but all of them are AFTER triggers, and it is large DB with many tables, views and stored procs, and it been used from several processes.

I added a log table and triggers like this 

Create Table [dbo].[Log_Test_IP]
(
  [Action] varchar(10),
  [IP] varchar(40),
  [IPType] varchar(6)
)
GO
Create Trigger MYTR_Log_Test_IP_INS On [dbo].[Test_IP] After insert AS
BEGIN 
   insert into  [dbo].[Log_Test_IP]([Action],[IP],[IPType]) 
       select 'Insert', [IP], [IPType] from inserted 
END
GO
Create Trigger MYTR_Log_Test_IP_DEL On [dbo].[Test_IP] After delete AS
BEGIN
   insert into  [dbo].[Log_Test_IP]([Action],[IP],[IPType]) 
       select 'Delete', [IP], [IPType] from deleted  
END
GO


Now I'm getting to the interesting part: when I directly insert to the Test_IP table I can see the Insert trigger is working, but when it works regulary from an application or service (which I have no idea what it does) I don't see any Insert records in the log table, I can only see the 'Delete' records even though it was enpty in the start.

My conclusion is that there is some way to bypass the triggers, there are many triggers and stored procedures in the DB and I have no idea where to look.

So, my question is how can you bypass the trigger?
Triggers will not run in a couple of scenarios. 

1) Obviously if the trigger is disabled

2) If the trigger is marked as NOT FOR REPLICATION and the DML is issued by the replication Distribution Agent.

3) If the user has ALTER TABLE permissions and is performing a BULK INSERT, BCP or SqlBulkCopy, etc with the FIRE_TRIGGERS option disabled.