AGI (buffer?) problem

When an AGI script is started, before any of its code is executed, it sends on stdout to Asterisk some junk information, depending on the context.

AGI Rx << Jun 5 07:17:07 WARNING[28118]: asterisk.c:806 ast_set_priority: Unable to set normal priority
AGI Tx >> 510 Invalid or unknown command

This is probably related to a buffer information which is somehow shared with the AGI system. Has anyone noticed this error too?

This problem occurs in version 1.2.7.1.dfsg-2. It does not happen in 1.2.0.dfsg-5.