In DOS, the length of the command line is limited to 127 characters (via the 0Ah int 21 function). This is done due to the fact that 127 bytes are allocated for it in the PSP. In DOSbox, the user can enter commands of unlimited length with unpredictable consequences.

Function 0ah (line input) of interrupt 21h is implemented incorrectly - it asks for input 1 character more than necessary. This is easy to convince yourself by reading the documentation, or by running a program that uses this function in real DOS.