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It also allows you to pick it mutiple times.
The pick it multiple times option is normal for certain techs - the warfare tree has at least two of them (refined training and advanced tracking), and the civ tree has refined housing in addition to the one you mentioned.
But I didn't notice that it didn't work. I'll try to corroborate.
It seems to be working for me. One fertile ground was giving me 42 food when normally it gives 15 IIRC.
Try taking a few of the farming techs then delete a fertile ground farm and see how much your food/turn changes to test it.
Researching the tech didn't immediately increase my food/turn which it should have if working correctly. I also got 42 food from a farm (precisely that ammount) though I had a granary, and a game hunting thing and was using the +food bonus faction. which sounds about right (rounded up). 15x2 +50%x15 +25%x15
It increases on the turn following research completion.
Except it doesn't. I've just confirmed this. The bonus from the food production faction is 50%, gardens were giving 3. They continued to give 3 regardless of how many refined foods I researched.
I've also noticed that the repeatable researches didn't work correctly. In fact, the more I researched the combat tree, the smaller I had to make squads! At first I lost companies (they cost as much as one unit, but took the full 10 unit time), then I lost squads and was down to parties as the biggest I could actually make and get multiple units out of.
Because it's advanced farming, not advanced gardening 
Just test it out already.. I already confirmed it with the farm. It gave exactly how much it should have given if I didn't research anything, and I researched the refined farming twice. Your free to keep not believing me though. I'm done with this topic.
We have and your report was not reproducible. Testing with one city and only a single farm, while researching intensively and choosing refined farming every time it appeared (8-10 times total each attempt before memory leaks stopped the test) granted an increase of 1-2 food each time, which is exactly as expected for a 10% bonus on a base of 15 food per farm.
The results were the same as Pariden (the food bonus faction) and as another faction. So if you are indeed not getting anything from the research, it must be some special case and we'll need more detail and a savegame to confirm it.
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