Hi, guys, It’s me again with another question. Based on what I had read in some of the postings, I bought an Oak in D. Love the tone, but…there is a wee quirk I wanted to ask about. When I go into the second octave, it just isn’t stable. I don’t know the exact term to use to describe what happens. D, E and F# are fine. The trouble starts with G, and gets worse the higher I go. The tones feel very unstable, they tend to break into the next lower octave, or occasionally jump about a 5th higher. I am working on breath control, emboucher control, and just plain hearing in my head the sound I want. Nothing seems to work. Is this a characteristic of the Oak whistle? When I do the same thing on my Clarke and Generation, that octave is nice and stable. Please advise.
Well out of the three cheapie whistles I initially bought Gen, Oak, Acorn, the Oak was actually the most stable, but my Clarke’s are better than any of them. Part of it is breath control as I’ve learned to play all of these better, but none are truly playable for me yet, unlike the Clarkes - two D’s and a C. I’m still working on it though and learning my own breath control and etc.
I also have two susato that have less of a problem with the octaves, but very different breath and embouchure requirements.
I’m just ordered a Freeman Tweaked Generation which I’m hoping will be much better than any of the three cheapies.
I think you’re discovering, first hand, the variabilities of the different whistles. Breath control is most likely the culprit, but you can bet if you tried a dozen more brands of whistle, you’d run into it again. Most important is to stick with your whistle. Overcoming the difficulties is what makes us good players. Hang in there!! 
Maybe take a look at the tweaking methods on the main website page. I love my Oaks and I usually take them apart, run super fine sandpaper through the blade area to clean them up, and stuff a little blue tack in the back, and those types of issues seem to get better for me.