We had a similar problem with our old oven. I think it was just that it was too hot at the top. The cupcakes would always be too hard on top and would kind of rise in an odd direction as well. Once we moved into our new house it stopped happening.
I saw an interesting oven test in Cook's Illustrated a while back to get an idea of what your oven is doing. I don't know if it will help test how how the top of the oven is but it might!
Basically the simple test was so take a loaf of slices bread (probably white as wheat had a bit more natural color) and put down a layer of slices, one next to the other. This forms a grid essentially. Then when you turn on your oven and the bread begins to toast, you'll be able to see if it's significantly hotter in one area or another as the bread will have a harder toast.
In the case of top or bottom, you may be able to get an idea if the top of the bread is more brown than the bottom.
I haven't tries this out myself yet but I've been meaning to!
This happened to me when I started to make cupcakes! I understand how frustrating it is and no matter what recipe you use it always produces a hard shell. If you leave your cupcakes for around half a day on the table, the tops of the cupcake will oxidise with the air and will therefore soften, trust me it works and also instead of baking at 180 degrees celsius, I bake at 150.
This happens me all the time until.. I found the solution... I used to bake in an electric oven.. but i found the cupcakes were inedible they were so hard! I now bake with a gas cooker and my baking is flawless if i do say so myself!... this is not just my mad notions... its been backed up and verified by a good few ppl I know. one elderly lady actually said to me, of course thats why and that she could have told me that "ages" ago!!
Another problem ,might be a fan oven - which are electric anyway - the fan dries stuff out. If it's a small oven, the top will be too close to the top of whatever you;re baking (like my microwave/fan oven/grill combination. My real oven (gas) was broken once and i promised someone a cake. I did it in the electric one (with only the oven function on, not the grill or microwave) and the top got overcooked, not enough height in the oven.
Try and go for Commercial gas Cookers (electric) or Electric Convection ovens. They contain special fans that circulate the heat all over the ovens proportionally. Therefore, there is no chance of unequal textures or taste.