Partial 850 Brake lights?

[robbo]

Yesterday I discovered another of my Volvo's fine features, the bulb failure light. It came on whenever the brake pedal was pushed. Simple enough, just replace a brake light bulb and the failure lamp went out. The particular bulb out was in the same module as the turn signal bulb in the back of my 96 wagon (behind the speaker). When poking around in the back of the car I noticed there were dual filament bulbs in the lower module and assumed they must be brake light lamps as well. The brighter of these filaments do not illuminate when the brakes are applied, just the tail light function works.
So, now all bulbs seem to satisfy the car's bulb failure feature, and I have brake lights functioning on both sides of the car and the third light in the gate. Shouldn't there be more than just one brake lamp per side? I did turn the daytime running light feature on recently, connected?