autocomplete idiosyncracies

[xzqx]

Has anyone noticed that emacs sometimes behaves differently regarding
autocomplete? For instance, suppose I have a directory containing the
following files:

blah
blahblah
blah-blah
blah-1

If I C-x C-f and navigate to this directory, then hit space ONCE, I
see:

Find file: ~/etest/blah

If I hit space again, I see:

Find file: ~/etest/blah-

If I hit space again, I see that, plus the completions list: blah-1
and blah-blah. If I'm not thinking, sometimes I forget that files
called 'blah' and 'blahblah' even could exist.

Does anyone know if there is a way to tweak this behavior? Many
websearches have come up empty. Thanks in advance,

Anne