As you have implied, as a failed transporter, such signals would not be anything unusual. Any proper teleFRAG unit, (which is really stretching logic here), would scan the area beforehand, sending back signals regarding its readiness for transport, or the successful completion of transport.
Essentially, for the operation in question, the teleFRAG would have to operate as a proper teleporter for a moment, and then follow its perverted purpose after. The unit would scan for the appropriate object, retrieve it, and then send through the same beam pattern the mixed message that results in the sub-atomic disorder so familiar to us.
It's simply the old stage-magician's trick for disappearing, a little flash and bang, some quick stepping, and then the big finish.
Room breaching, if I'm reading you right, is merely programming a little delay in the normal decay pattern of the teleFRAG. The transported object is stable until the beam collapses, and normal and non-normal matter get to mix. Also effective in delaying detonation patterns is changing the power of the explosion. What you described would take a cracker-jack technician, but that's what genius and simulation chambers are for.