For example, item key is external["test","dads","dasdas","da[aa]asd"]:
3328:20121016:213833.778 In substitute_simple_macros() data:'external["test","dads","dasdas","da[aa]asd"]'
3328:20121016:213833.778 In get_value() key:'external["test","dads","dasdas","da[aa]asd"]'
3328:20121016:213833.779 In get_value_external() key:'external["test","dads","dasdas","da[aa]asd"]'
3328:20121016:213833.779 In zbx_popen() command:'/etc/zabbix/externalscripts/external 127.0.0.1 "test","dads","dasdas","da[aa'

Zabbix server cuts the last argument.

The problem occurs only on Zabbix 1.8!