Service Broker's SEND statement causes security context switch

We have triggers in multiple tables that will send messages to a Service Broker service upon INSERT, UPDATE and DELETE operations. These operations may be nested as parts of bigger, transactional operations in various different processes, with additional operations coming up after sending the messages but before transactions actually gets committed. Our users authenticate using SSPI (Windows Active Directory). Some legacy stored procedure have been setup with WITH EXECUTE AS OWNER clause so we don't have to worry about possible permission issues for whatever these procedures will do - including writing in tables described above. Yesterday, following up an update to one of our apps, it started logging a strange permission error on a very basic SELECT statement. I looked up the procedure (it happens to be a SQLCLR procedure) and it should indeed be running as its owning schema (dbo in this case, which happens to be mapped to sa user) and therefore have every possibly required permissions. I ran a Sql Profiler session while trying to reproduce the issue and noticed something strange: the SEND command caused LoginName to switch back to the domain user. From this point on, it's as if the EXECUTE AS OWNER condition in the head procedure was being reverted. Just to make sure, I disabled Service Broker on the database and did the exact same action. Sure enough, there was no more security context switch. What could possibly be the cause for this? Is this by design? Is it smh because it's invoked from within SQLCLR? As a reference, here is the declaring code for the head procedure:

CREATE PROCEDURE [dbo].[ps_SQLCLR_RunTicket]
	@ticket [nvarchar](128)
WITH EXECUTE AS OWNER
AS
EXTERNAL NAME [SomeAssembly].[SomeStaticClass].[SomeMethod]
GO

And here is a slimmed down version of the nested code that's calling out SEND:

-- This code normally is in a stored procedure that's invoked from a trigger

DECLARE @msg VARCHAR(MAX) = ''

SET @handle = NEWID();

BEGIN DIALOG CONVERSATION @handle
FROM SERVICE auditService
TO SERVICE 'receivingService'
ON CONTRACT auditServiceContract
WITH ENCRYPTION = OFF, LIFETIME = 600;

SEND ON CONVERSATION @handle
MESSAGE TYPE auditMessageType (@msg);

END CONVERSATION @handle;