Program: 13316
Project: 13316
Buggy source:
public static Object substVars(String val,final PropertyAccessor propertyAccessor,Delimiter delimiter,boolean doEscape){
  int stopDelim=-1;
  int startDelim=-1;
  if (!doEscape) {
    stopDelim=val.indexOf(DELIM_STOP,stopDelim + 1);
    if (stopDelim < 0) {
      return val;
    }
    startDelim=val.indexOf(delimiter.getStartString());
    if (startDelim < 0) {
      return val;
    }
  }
  StringBuilder parentBuilder=new StringBuilder(val.length());
  Stack<StringBuilder> propertyStack=new Stack<StringBuilder>();
  propertyStack.push(parentBuilder);
  for (int index=0; index < val.length(); index++) {
switch (val.charAt(index)) {
case '\\':
{
        if (doEscape) {
          index++;
          if (index < val.length()) {
            propertyStack.peek().append(val.charAt(index));
          }
        }
 else {
          propertyStack.peek().append(val.charAt(index));
        }
        break;
      }
case '&':
{
      if ('{' == val.charAt(index + 1) && val.charAt(index) == delimiter.getStartChar()) {
        propertyStack.push(new StringBuilder(val.length()));
        index++;
      }
 else {
        propertyStack.peek().append(val.charAt(index));
      }
      break;
    }
case '$':
{
    if ('{' == val.charAt(index + 1) && val.charAt(index) == delimiter.getStartChar()) {
      propertyStack.push(new StringBuilder(val.length()));
      index++;
    }
 else {
      propertyStack.peek().append(val.charAt(index));
    }
    break;
  }
case DELIM_STOP:
{
  if (propertyStack.size() == 1) {
    propertyStack.peek().append(val.charAt(index));
  }
 else {
    String variable=propertyStack.pop().toString();
    if ((index == val.length() - 1) && propertyStack.size() == 1 && parentBuilder.length() == 0) {
      Object substValue=getSubstituteValue(Object.class,variable,propertyAccessor);
      if (null != substValue) {
        return substValue;
      }
 else {
        propertyStack.peek().append(delimiter.getStartChar()).append(variable).append(DELIM_STOP);
        return propertyStack.peek().toString();
      }
    }
 else {
      String substValue=getSubstituteValue(String.class,variable,propertyAccessor);
      if (null != substValue) {
        propertyStack.peek().append(substValue);
      }
 else {
        propertyStack.peek().append(delimiter.getStartChar()).append(variable).append(DELIM_STOP);
      }
    }
  }
  break;
}
default :
{
propertyStack.peek().append(val.charAt(index));
}
}
}
for (int index=propertyStack.size(); index > 1; index--) {
StringBuilder top=propertyStack.pop();
propertyStack.peek().append(delimiter.getStartString()).append(top.toString());
}
return parentBuilder.toString();
}

Fixed version (ground truth):
public static Object substVars(String val,final PropertyAccessor propertyAccessor,Delimiter delimiter,boolean doEscape){
  int stopDelim=-1;
  int startDelim=-1;
  if (!doEscape) {
    stopDelim=val.indexOf(DELIM_STOP,stopDelim + 1);
    if (stopDelim < 0) {
      return val;
    }
    startDelim=val.indexOf(delimiter.getStartString());
    if (startDelim < 0) {
      return val;
    }
  }
  StringBuilder parentBuilder=new StringBuilder(val.length());
  Stack<StringBuilder> propertyStack=new Stack<StringBuilder>();
  propertyStack.push(parentBuilder);
  for (int index=0; index < val.length(); index++) {
switch (val.charAt(index)) {
case '\\':
{
        if (doEscape) {
          index++;
          if (index < val.length()) {
            propertyStack.peek().append(val.charAt(index));
          }
        }
 else {
          propertyStack.peek().append(val.charAt(index));
        }
        break;
      }
case '&':
{
      if ('{' == val.charAt(index + 1) && val.charAt(index) == delimiter.getStartChar()) {
        propertyStack.push(new StringBuilder(val.length()));
        index++;
      }
 else {
        propertyStack.peek().append(val.charAt(index));
      }
      break;
    }
case '$':
{
    if ('{' == val.charAt(index + 1) && val.charAt(index) == delimiter.getStartChar()) {
      propertyStack.push(new StringBuilder(val.length()));
      index++;
    }
 else {
      propertyStack.peek().append(val.charAt(index));
    }
    break;
  }
case DELIM_STOP:
{
  if (propertyStack.size() == 1) {
    propertyStack.peek().append(val.charAt(index));
  }
 else {
    String variable=propertyStack.pop().toString();
    if ((index == val.length() - 1) && propertyStack.size() == 1 && parentBuilder.length() == 0) {
      Object substValue=getSubstituteValue(Object.class,variable,propertyAccessor);
      if (null != substValue) {
        return substValue;
      }
 else {
        propertyStack.peek().append(delimiter.getStartString()).append(variable).append(DELIM_STOP);
        return propertyStack.peek().toString();
      }
    }
 else {
      String substValue=getSubstituteValue(String.class,variable,propertyAccessor);
      if (null != substValue) {
        propertyStack.peek().append(substValue);
      }
 else {
        propertyStack.peek().append(delimiter.getStartString()).append(variable).append(DELIM_STOP);
      }
    }
  }
  break;
}
default :
{
propertyStack.peek().append(val.charAt(index));
}
}
}
for (int index=propertyStack.size(); index > 1; index--) {
StringBuilder top=propertyStack.pop();
propertyStack.peek().append(delimiter.getStartString()).append(top.toString());
}
return parentBuilder.toString();
}