Ah, the flickr one was a video (with my scripts filter, I only saw a still image, at first). You know, describing a reproduction procedure with words is often faster and easier...
Well, yes, I could repro this now; it is a bug introduced in v1.28.2.57 (the previous versions work fine in this respect). I already spotted it and fixed it for next week's release. If you compile the viewer yourself, simply change line 9562 of linden/indra/newview/llpipeline.cpp to read:
I.e. replace "RenderWaterReflections" with "sWaterReflections" in that line...
In the mean time, simply keep water reflections on with "Terrain and trees" in the combo box (i.e. the lower setting): the difference in the FPS rate with no reflection at all is almost negligible anyway.