Why is the variable behaving so strangely in the for loop?

Question

cmd/bat

Hello!
The variable in a script behaves strangely. There is a file in which the paths to the files are entered line by line:

"d:\test\file1.txt"
"d:\test\file2.txt"
"d:\test\file3.txt"

There is a bat -script that reads the path line by line from the file, changes the drive letter in it and passes it on:

SetLocal EnableDelayedExpansion
FOR /F %%i IN (d:\test\tmp.txt) DO (
   SET str=%%i
   SET str=!str:~2,-1!
   echo %str%
)

The problem is the strange behavior of the %str% variable. It can always be empty , it can take the value as it should, i.e. " :\test\file1.txt :\test\file2.txt :\test\file3.txt ", or it can always be :\test\file3.txt
The same script on another server always runs correctly. Both servers are 2012R2Std 9600build.
Tell me what could be the problem?

Answer 1

Replace inside the
echo %str% loop
with
echo !str!

Answer 2

Thank you very much! Using an exclamation mark (!) instead of a percentage (%) worked!
Can you clarify why this particular syntax is used in this case?
It turns out it is connected with the mode of binding of execution time?