When finished the rough sanding of your pipe, let it rest for a day or two.
Now, the simple rationale. Put some drooling countermeasures before looking at this picture:
![Image](http://www.scandpipes.com/log/pipes/databasebilleder/full/231-11.jpg)
After you stop drooling at that birdseye, take a deep look. The surface is not regular! The birdseye seems to add some texture. My guess is different density fibres absorbs moisture at different rates, and even when exposed to temperature changes, it expands or contracts at an uneven rate, too.
You can draw a paralel between a birdseye-full surface and a tightly-bound cluster of wooden sticks.
Now, this will happen to all birdseye surfaces; get used to it. However, if you allow your recently shaped pipe to rest for a while, your pipe will maintain its smooth glass-like appareance for a longer time. If you don't, local environmental factors can alter a recently-finished pipe in no time. In my opinion, it is okay for an estate pipe to have a bumpy appareance after a few years (like the Nordh in the picture.) However, I don't think the same about a recently finished pipe; let your briar rest!
Disclaimer: all of this half-assed theory is, of course, product of my own observation. Don't go around calling me names, please.