Exetools - Unwanted code added while assembling on Olly

In the executable provided in chapter 6 of Lena's tutorials I see the following code which is responsible of setting the variable that will be used for checking if the app is registered or not:

Code:

; AL contains 0 from a previous call to a custom function,

; which is the one that checks if the app is registered or not.



005C2BF6    .  8B15 8CEB6000     MOV EDX,DWORD PTR DS:[60EB8C]

005C2BFC    .  8802              MOV BYTE PTR DS:[EDX],AL

005C2BFE    .  A1 8CEB6000       MOV EAX,DWORD PTR DS:[60EB8C]

005C2C03    .  8038 00           CMP BYTE PTR DS:[EAX],0

005C2C06    .  75 0D             JNZ SHORT pcsurgeo.005C2C15

005C2C08    .  E8 6307EEFF       CALL pcsurgeo.004A3370

After that code the pointer at 60EB8C is checked several times to make decisions on to whether to display register messages/buttons or not.

In the tutorial file I see Lena changing this:

Code:

005C2C03    .  8038 00           CMP BYTE PTR DS:[EAX],0

005C2C06    .  75 0D             JNZ SHORT pcsurgeo.005C2C15

to this:

Code:

005C2C03    .  8038 00           MOV BYTE PTR DS:[EAX],1

005C2C06    .  75 0D             JMP SHORT pcsurgeo.005C2C15

So i thought that i could achieve the same by fixing the MOV that is before those two lines like this:

Code:

005C2BFC . 8802 MOV BYTE PTR DS:[EDX],1 ; Force it to be 1

But as soon as i do that the whole code changes to this:

Code:

005C2BF6    .  8B15 8CEB6000     MOV EDX,DWORD PTR DS:[60EB8C]

005C2BFC       C602 01           MOV BYTE PTR DS:[EDX],1     ; Changed line

005C2BFF       8CEB              MOV BX,GS    ; automatically added

005C2C01       60                PUSHAD        ; automatically added

005C2C02       0080 3800750D     ADD BYTE PTR DS:[EAX+D750038],AL

Can somebody explain me why does that happen?