item "unsupported" although zabbix_get works and no log errors?

[sean]

I've a custom item that works fine from the command line, but not from the GUI, where it says "Not supported" and then disables it.

zabbix_agentd.conf"
UserParameter=custom.foo,ps -ef |wc -l

From the server:
/usr/local/bin/zabbix_get -s myhost -k custom.foo
92

In the client log:
542:20130426:103403.497 Processing request.
542:20130426:103403.498 Requested [custom.foo]
542:20130426:103403.498 In zbx_popen() command:'ps -ef |wc -l'
542:20130426:103403.499 End of zbx_popen():7
724:20130426:103403.499 zbx_popen(): executing script
542:20130426:103403.513 In zbx_waitpid()
542:20130426:103403.513 zbx_waitpid() exited, status:0
542:20130426:103403.513 End of zbx_waitpid():724
542:20130426:103403.514 Run remote command [ps -ef |wc -l] Result [2] [92]...
542:20130426:103403.514 Sending back [92]

Server is v2, client is v1.8.
For the server items have tried using different types: character, numeric/decimal.
Latest data is always 0
Server logs:
item [myhost.ch:custom.foo] became not supported: Not supported by Zabbix Agent

Mystified...