Depending on the way I enter numbers in the password field, the launcher accepts or refuses my password :
Shift + touches above the letters (Shift being required since it's an AZERTY, and Caps Locks under Linux capitalizes characters instead of entering numbers) : works fine.
Num. Locks + pavement : works fine.
Shift + pavement (no num. locks, of course) : refused.
It may sound like a very minor issue, but I only found out how it worked by trying everything out of desperation.
Hope the information was understandable. Thanks for your work