Overwintered plants not feeling well :(

[Mayloa]

After harvest last season I decided to give overwintering a shot, I had two healthy looking Cayenne plants that I didn't like throwing out anyway.
I cut the main stem just over the second node, And it managed to grow new foliage quite fast. As we got over to winter the leaves started to curl, with the tip curling downwards. I didn't worry much about this though as I've been told (or read somewhere) that this is normal among evergreen plants. It's suppose to be a defence mechanism to avoid too much transpiration.

Anyway they have managed just fine throughout the whole winter period, just sitting in my windowsill without any extra lighting. I've given them about 50-75% dosage of the same nutrients as they had during the summer period.

Since Christmas (or around there) the tips of the leaves started to turn dark, and then into brown and started to show signs of mould. (Only the tips of the leaves) Both new and old leaves show these signs. I check them for bad looking leaves and remove them asap, in case it would spread to other plants or such.

Is this something you've seen when overwintering plants too? If so; is it common?

[PP]

I'm not sure if this could cause the symptoms, but the amount of nutrients seems high for small overwinterted plants without extra lighting. The soil should be kept quite dry (on average) ja and a small amount of nutrients is enough.

[Mayloa]

They've grown quite a bit though, as I cut them down quite early in the autumn. So I can't say that they are small any more 
And about nutrient levels, I should probably add that I did put 50-75% nutrients in the water when watering.
But I didn't water them as often as in the summer period, seeing as transpiration isn't as high during dark & cold periods.