Has your cake ever browned on the INSIDE?!

Hi,

I've been baking for years, but baking in my new gas oven has me stumped and I can't seem to find a solution for it.

I baked a rhubarb upside down cake and while the cake looked beautifully browned on the outside, and the skewer inserted came out clean, when I cut a slice of the cake, the cake was brown on the inside! I've made this cake several times and it's been perfectly white each time. I'm not sure what could have happened.

How can I combat this?

Thank you!