First of all thanks again for all the great work on foobar2000!

I've upgraded v0.9.5.1 to v0.9.5.2 as I always did since v0.9 but now I noticed the introduction of a new problem. When listening to online aac-radio the first 1 to 2 secs the sound is horrible, it's like some music information is missing. After this start all sounds ok. This happens only with AAC and at all rates but not with mp3 stations. Former fb2k version didn't exhibit this behaviour, just only sometimes the high frequencies jump in after 1-2 secs without this horrible distortion. Anyone else noticed this change?

Thx in advance.

Confirmed. Some light distortion can be heard for a short moment. Here an example: http://friskyradio.com/frisky_aac.m3u

Confirmed, but that happened with every foobar2000 version I've used to listen to (HE-)AAC radio streams with.
Maybe (I'm only guessing here!) the information that it is an HE-AAC stream is only transmitted every two seconds, and only when foobar recognizes this info, the SBR decoder kicks in.

Yeah, this is because of the SBR data. SBR contains headers that use up some bits even when the data is usually consistent over multiple frames (usually the data never even changes), that's why SBR encoders don't have to send this data every frame, but for random access purposes they send it every now and then. Starting the digital radio case is basically the same as random accessing a frame and the SBR is not decoded until the first header is found. I did make some changes to make this part of the decoder more robust for bitstream errors. We had some crashes in internal testings.

BTW: you will not notice this behavior when seeking in foobar because foobar basically starts decoding a little bit before the seek point and then starts outputting from the seek point.