All the heat DOES come from the bottom. It took me a while to adjust to my gas oven, but now I absolutely love cooking with gas. I found that just adjusting cooking temps and times was perfectly effective. Bring your temp down by 25 degrees or so, and check on your food about 15 minutes before the suggested time.

Of course, there might be something actually wrong with your oven, but mine was just an adjustment in my cooking, and now everything comes out fine.

Gas ovens do bake differently. Things tend to get more brown on the bottom and I do back off my times. I also use a thermometer to get a basic sense of the temperature.

But when my pizza set off the smoke alarms because the bottom was black and the cheese on top hadn't melted I knew there was more going on....I had to have my heat probes replaced.

Try setting a pizza stone on the heating element, if it's encased in metal. But this sounds serious enough to bug your landlord over.

You might also try baking on a higher rack in your oven. That way, your food is farther from the bottom heating element and the convection effect is stronger, cooking the bottom less and the top more. If you're interested in the nerdy science of it, or at least want to look at some pictures explaining the concept, check out this post from Serious Eats. The author is specifically addressing pizza cooking, but the science is the same no matter what you're sticking in your oven.

If the oven's not broken there are a couple of way to mitigate for the uneven heat. First is to place the rack in a higher slot than you normally would, to get the pan farther from the direct heat source. Second would be to place another rack with an old cookie sheet below the one you are using for baking. This deflects most of the radiant heat from the bottom and forces the convective heat around to the sides of the oven where it will flow around you pan more evenly.

If you don't have a top element, make sure there is plenty of room around your pans for hot air to flow around to the top of the oven.

I think the diagrams in this serious eats article are great for explaining the heat flow in an oven and their conclusions might be useful in you cupcake problem.

If the oven isn't actually broken, or the landlord is slow to fix it: Ditto on the pizza stone. Also consider Silpats for your baked goods, and silicone pans for your cupcakes.

I'm with Katlian!

To keep my cookies from over browning on the bottoms I put another cookie sheet on the shelf below the cookies pan and watch them closely.

Another consideration: Are your baking pans dark? I found that food browns more or even burns easily when baked in dark pans. When I use lighter colored pans, that problem goes away.

I have the same kind of stove. I really haven't had any problems except with baking cookies. I do generally put things higher in the oven and check things early. Good quality bakeware for cakes and the like seems to work for the most part. I'll have to give the silpats a try for the cookies, (though the baking difficulty has helped me resist the temptation to whip up a batch!).

uneven heat in an oven is a feature not a bug. you can use the fact that the heat is rising from below in an enclosed box to your advantage.

if you cook near the bottom, the bottom will cook faster. good for braises. if you cook near the top, the reflected/collected heat will cook the tops faster, good for cookies. also, if you don't wait for the oven to preheat, the only heating that the food is getting for the first several minutes will be from below.

however, between the flame element and the bottom surface of a gas oven is a metal baffle that is supposed to disperse the heat a bit. basically a built in cookie sheet. after many years, the welds that hold that baffle on can conceivably weaken. In the oven I grew up with, after many years, it actually fell completely off and we had to get it re-welded. an oven stone will work fine for this, but they take forever to heat up.

but there's a reason many recipes specify "bake on top rack," "roast on bottom rack," "bake in upper third" etc.

Cookies should do great in a gas oven, the one time I had this issue I was using parchment paper on the pans and had two side to side, well the air circulation was completely destroyed (due to the parchment, it works fine without) and I ended up with charred bottoms.

Get the thermostat checked. Even after that, put a pizza stone (or unglazed quarry tiles) at the bottom of the oven and let them heat for 20 minutes or so before cooking; they really work to even out the heat. I keep my pizza stone in all the time and it has made a difference on several somewhat touchy ovens--I keep it in the oven we have now from sheer laziness even though it holds its temp very well.

I had this problem and it turned out that the gas was not distributing properly and therefore the flame was not even. At first I thought it might have been clogged and I took it out and checked it. When that didn't work out, I called the gas company. They sent someone out FOR FREE to check it out - and it turned out that the part where the gas enters the distributor (sorry, I have no idea what the parts are actually called) was not flowing fast enough and was of centered. A few adjustments and it was drastically improved.

Just do it yourself, don't wait around for a landlord. Just call the gas company.