Help for a complex RE

[Sergio Spina]

In the following ipython session:

> Python 3.5.1+ (default, Feb 24 2016, 11:28:57) 
> Type "copyright", "credits" or "license" for more information.
>
> IPython 2.3.0 -- An enhanced Interactive Python.
>
> In [1]: import re
>
> In [2]: patt = r"""  # the match pattern is:
> ...:     .+          # one or more characters
> ...:     [ ]         # followed by a space
> ...:     (?=[@#D]:)  # that is followed by one of the
> ...:                 # chars "@#D" and a colon ":"
> ...:    """
> 
> In [3]: pattern = re.compile(patt, re.VERBOSE)
> 
> In [4]: m = pattern.match("Jun at i Bun#i @:Janji")
> 
> In [5]: m.group()
> Out[5]: 'Jun at i Bun#i '
> 
> In [6]: m = pattern.match("Jun at i Bun#i @:Janji D:Banji")
> 
> In [7]: m.group()
> Out[7]: 'Jun at i Bun#i @:Janji '
> 
> In [8]: m = pattern.match("Jun at i Bun#i @:Janji D:Banji #:Junji")
> 
> In [9]: m.group()
> Out[9]: 'Jun at i Bun#i @:Janji D:Banji '

Why the regex engine stops the search at last piece of string?
Why not at the first match of the group "@:"?
What can it be a regex pattern with the following result?

> In [1]: m = pattern.match("Jun at i Bun#i @:Janji D:Banji #:Junji")
> 
> In [2]: m.group()
> Out[2]: 'Jun at i Bun#i '