You need to add an extra parameter indicating the parameters to be copied when the call is re-executed by dumb module:
.*=dispatch call.execute;callto=dumb/;direct=sip/sip:54321@x.x.x.x;osip_X-Acct=${acctid};copyparams=osip_X-Acct
The 'copyparams' parameter is a comma separated list of parameters to be copied.