The function "printf()" does not belong to the list of async-signal-safe functions.
See section "2.4.3 Signal Actions" from the document "2.4 Signal Concepts".
http://opengroup.org/onlinepubs/009695399/functions/xsh_chap02_04.html#tag_02_04_03
The corresponding calls should be deleted from your functions "sigchld_handler" and "sigquit_handler".
http://gqlplus.cvs.sourceforge.net/gqlplus/gqlplus/gqlplus.c?revision=1.9&view=markup
Thanks for reporting.
Fixed and will be included in the next release.
May the source be with you,
Jess