Pocketsphinx try to recognize word even if they aren't in the grammar file

[thierry96]

Hello,
I'm testing pocketsphinx with digits recognition only. I noticed that if i say something else which are not in the grammar file, i always get a matching between what i'm saying and the digits in grammar file, even if i don't pronounce the correct digit.
I would like to know if there is a way to fix that and also i would like to know if i can lower the microphone volume because even if i blown, pocketsphinx try to display some incorrect value.
Thanks in advance