I had a similar problem (see my thread about Squeezebox Boom dropping
Internet Radio), but not identical to yours, using radio stations via
SqueezeNetwork. Don't know about the NPR issue (I avoid those guys like
the plague) but it was repeatable on the stations I use.
Just yesterday I discovered
Internet radio seems to work well unless the radio station broadcasts a
header ("internet streaming is brought to you by..."), which is quite
common on NPR stations. The header is played successfully, then I get a
"rebuffering" message, and then the header replays after about 20-30
seconds. This
