Tabbing at the beginning of a command with words after it adds space

[jgross@mit.edu]

If I tab from the middle of a command that is already completed, for example st|artup zlog (where | represents where the cursor is), then I get startup | zlog. If I tab from the beginning of a command, e.g., |startup zlog, then I get |startup zlog with an extra space between startup and zlog.