I was yelled at today by a CSR at the 1K counter for illegal back-to-back ticketing.

I have a B-fare booked that looks as follows: beginning of April I flew DEN-AMS, and somewhere in July I will be flying BRU-DEN. I booked it this way for accounting purposes.
I also have a AMS-DEN-AMS trip this week that I only booked about two weeks ago.
According to the agent, that's back to back ticketing, and it's illegal.
Was she right? I have no intention of cheating the system. Besides, the city pairs don't even match up and my B-fares are expensive.