Version ID : 350m1(Build:2)
System Ubuntu 12.04 (up to date) in VirtualBox
Langage : French (this may be important)
Using numeric pad to enter numbers
Enter : 2 displays 2
Enter : 2.0 (2 dot zero) displays 01/02/00
Lets convert this to a number format (instead of date)
Format/cellule categorie=nombre, format=standard and OK
Cell now displays.... 36557
Enter 2.1 in the same cell
Cell now displats ... 40910
ok ok i should have typed 2,5 (2 coma 5)...
but this is a spreadsheet bug source
This is not a bug. This is a feature called partial date input. There are some date acceptance patterns based on your local that transform input automatically into dates if they can't be numbers.
Dates are internally nothing else than numbers so everything here is working correctly.