This turns out to be a configuration problem. Appearently, odbc.ini has to be encoded in UCS-2 or UCS-4 according to the informix documentation. This turns out to be how the unixODBC consumes the configuration file.
nearing the end of odbc.ini, there is an [ODBC] section, uncomment the UNICODE option like so
; ; UNICODE connection Section ; [ODBC] ;uncomment the below line for UNICODE connection UNICODE=UCS-2 ; ; Trace file Section ; Trace=0 TraceFile=/tmp/odbctrace.out InstallDir=/extra/informix TRACEDLL=idmrs09a.so