Hi. Most likely, you've got a blown fuse, or too much corrosion on one fuse's contacts. But the Volvo's separation of left and right side lights isn't peculiar (except compared to "a Couple of Old Chebbies"), and is the norm for European cars -- one of my M-Bs, imported directly from Europe in the '80's, is the same way.
The reason, in case you're interested, is that in Europe, cars have light switches that, when the engine is off, allow the driver to selectively light just the right or the left side parking lamps of the car -- one of my M-Bs is a gray market vehicle, and has such a light switch. And such separation, as you can now see, requires separate fuses for each side. Even thought USA-version Volvos don't have the light switch, their car's wiring harness retains that circuitry.
And the reason for this European feature is that, in many small towns in Europe, cars can park on the sides of narrow streets, but when they do so, at night they must leave their lights on all night long. However, to save their batteries, they are only required to light the lamps on the "road" (i.e., car traffic) side of their car, and this saves their batteries by halving the drain that would occur if they left both sides of the car lit.
Hoped this helped.
Have a great Thanksgiving.