Oracle Label Security - debugging

I'm just getting started attempting to implement Label Security to move our product from a single to a multi-tenant architecture. What is the best way to debug Label Security problems? I've tried trace levels 10730 and 10060 using commands like this:

ALTER SESSION SET EVENTS '10730 trace name context forever';

but didn't get a trace file. 

I did get a trace file for a 10046 trace. Here's a SQL statement that resulted from that trace:

SELECT  "C1","MI_ROWLABEL_3" FROM "MT_DB1"."T3"  "T3" WHERE (1=2 ) 

I didn't specify that 1=2 predicate, so where is that coming from?

Any help would be greatly appreciated.