tile yield drops when I buy the tile

[Worldsapart]

So I drop my new city next to some pretty hills with 3 hammers on about 5 different tiles. The super huge problem is that once I plop down the city those tiles change from 3 to 2, I of course didn't notice this until after I built the quarry, and really noticed it when I bought a new tile with gold. 3 hammers, buy the tile, 2 hammers. What's going on? I'm assuming this is a bug. If it's not, then I'd really like to know what's going on.

 

[WuphonsReach]

Maybe you're seeing the yield icon bug?

[Bug] Hex yield icons incorrect
http://forums.civfanatics.com/showthread.php?t=383564

Was it just the yield icons that were incorrect, but the mouse-over tooltip was the same? Had you had a golden age after initially exploring the tiles but before going back to settle?