trascoding mp4a SBR to mpga downmix'es to mono

Hello,

i have to transcode MPEG 2 TS with mp4v and mp4a with SBR to MPEG 2 TS with mpgv andmpga, and allways mp4a SBR downmix'es to mono on mpga.

Problem persist with 1.0.6, 1.1.4, 1.2.0, 2.0.0

Debug output attached.