pcomplete-termination-string

pcomplete-termination-string is a variable defined in `pcomplete.el'.
Its value is

" "

Documentation:
A string that is inserted after any completion or expansion.
This is usually a space character, useful when completing lists of
words separated by spaces. However, if your list uses a different
separator character, or if the completion occurs in a word that is
already terminated by a character, this variable should be locally
modified to be an empty string, or the desired separation string.

You can customize this variable.