Strange behaviour on a numeric field in a DSPF

I  happened to notice this strange behaviour on a numeric field
defined in a display file after one of our customer complained about
this.

The numeric field is coded as follows in the DSPF

      A                                 13 42'Days 1  . . . . . .'             
      A                                 13 62':'                               
      A            WSDAY1         5Y 2B 13 64EDTCDE(4)                         

If I enter 1 and hit enter the field gets populated with  1.00 (this
is as expected)
Days 1  . . . . . . :   1.00 

If i come back to the same field and put 1 in the 1st postion and h

Days 1  . . . . . . : 3 1.00

and hit enter without using field exit to blank the rest of the field
the display gets populated with 301.00  (not expected )

Days 1  . . . . . . : 301.00 

Have any of you noticed this behaviour before ? Is there a way to
prevent this from happening other than using the CHECK(FE) keyword ?

Thanks

Krish