pg_dump 9.2.x command does not work with pg_dump 9.2.3

This is how i used to create all the time backups of my databases with PostgreSQL 9.2.x:

pg_dump -Fc -Z 6 -U postgres mydatabase > 2013-xx-xx_xxxxx.db

However on a machine where PostgreSQL with version 9.2.3 is running I get all the time the error “too many command line arguments” starting with “-Z”. If I remove -Z he is complaining about “-U”?
What is wrong?

Okay there is definitely sth. wrong. I removed argument for argument until i just started pg_dump. Then i added argument by argument and it worked. So I opened another command line window and tried the same: First “too many arguments”, after calling only “pg_dump” and adding further arguments it worked…