Not Fixed, no stacking.

Will investigate this issue

I had same problem that i got long time to get POS rewards, my minting weight was greatly over the network weight and expected time to earn reward was 0s. I don't remember days when i finally start to get rewards. Now i have moved my coins from one wallet to another and counting how long it takes to get POS rewards.
Note, if you use your coins then they start to mature all over again.