Strawberries ripen on the bottom but stay white on top, why?

I've done a lot of Googling and searching permies for info on this.  

Our garden is in a clearing in the redwood forest.  We have a ton of strawberry plants in many beds, and most of them do amazingly well, as this is native strawberry habitat.  However, our beds that are near the edge of the forest do this weird thing where although the berries are huge, only the bottom half-ish of the berry ripens, and then it starts to rot eventually.  It's not just color, the top half isn't ripe either, doesn't taste as good as the strawberries from other beds that turn fully red.

I suspect it's due to being close to redwoods or other forest trees (tanoak, doug fir), and there are tree roots in the soil under these strawberries.  I recall not really having this problem in the strawberries' first year, probably because we had just dug these beds and they weren't already colonized by redwoods.  They did have the problem in the second year, and now it's the third year and they still have it.

I wonder if there's some way to help it anyway, like maybe the redwoods are taking a particular nutrient and I could supplement that, or something.  Anyone seen this in other environments or have an idea what it might be?  

It's meant to be due to excessive heat as the berries develop.  Are they Cavendish by any chance, they are especially prone to it.