Steps:

1. Create Java class MyTest.java:
package com.example;

/**
 * {@snippet class="Test" region=reg:
 *
 *
 * void two() {}}
 */
public class MyTest {
}
2. Create the Test.java snippet in snippet-files:
class Test {
    // @start region=reg
    // @replace region substring="one" replacement="two"
    void one() {}
    // @end
    // @end
}
3. Run javadoc tool
javadoc.exe --snippet-path=snippet-files MyTest.java

Expected result: either no errors, or an error message which clearly shows what should be fixed

Actual result: error message that says about content mismatch, while the rendered content shown in error message is byte-to-byte the same.

Here's the complete output:

Loading source file MyTest.java...
Constructing Javadoc information...
Building index for all the packages and classes...
Standard Doclet version 21-ea+12-971
Building tree for all the packages and classes...
Generating .\com\example\MyTest.html...
MyTest.java:4: error: contents mismatch:
 * {@snippet class="Test" region=reg:
   ^
  ----------------- inline -------------------
  
  
  void two() {}
  ----------------- external -----------------
  
  
  void two() {}
MyTest.java:9: warning: use of default constructor, which does not provide a comment
public class MyTest {
       ^
Generating .\com\example\package-summary.html...
Generating .\com\example\package-tree.html...
Generating .\overview-tree.html...
Building index for all classes...
Generating .\allclasses-index.html...
Generating .\allpackages-index.html...
Generating .\index-all.html...
Generating .\search.html...
Generating .\index.html...
Generating .\help-doc.html...
1 error
1 warning