Xiph Tremor code for Ogg decoder

I'm using Xiph Tremor code for OGG-Vorbis decoder. When 1Khz base frequency with 0db amplitude input signal is given to OGG-Vorbis decoder, clipping is observed in decoded PCM output. Also in frequency analyzer tool, frequency spectrum of decoded PCM output has harmonic distortions. When same input is given to VLC player, output sound is good and frequency response of output is not having any distortions. Has anyone come across such behavior? any solution for this?