Problem with dynamic fields on simobject

I've written a save file system using the XML class in script. I create a simobject, assign some values on it, and pass that to a function to dump the dynamic fields to the XML. This works great, except in one case - if I add the value of $Sim::Time to SaveFileInfo.GameTime, then I can no longer retrieve the GameTime field - iterating through the dynamic fields no longer finds GameTime - but it does find a field named "CrossbowReloadSound" (obviously not from this object...)

Has anyone seen this kind of behavior before? It's like the dynamic fields have gotten corrupted. I am able to evaluate SaveFileInfo.GameTime + $Sim::Time in the debugger without a problem, and it gives the correct values.

*edit - it's getDynamicField that is returning the wrong field name (see function code below). Typing echo(SaveFileInfo.GameTime); returns the correct value for the GameTime field.

%fldname = %object.getDynamicField(%i);

new SimObject(SaveFileInfo)
{
   GameTime = 0;
};

function UpdateSaveFileInfo(%Comment,%Screenshot)
{
   SaveFileInfo.Location = MissionInfo.name;
   SaveFileInfo.Comment = %Comment;
   SaveFileInfo.Screenshot = %Screenshot;  
   SaveFileInfo.GameTime = SaveFileInfo.GameTime + $Sim::Time;   
   SaveFileInfo.MissionFile = $Server::MissionFile;
   SaveFileInfo.Game = $Server::GameType;
   SaveFileInfo.Type = $Server::MissionType;
   SaveFileInfo.Player = $pref::Player::Name;
   SaveFileInfo.ServerType = $Server::ServerType;
}

The XML with the bad field:

- <SaveFileInfo>
  <ServerType>SinglePlayer</ServerType> 
  <Location>Sorcerors Isle</Location> 
  <Comment>comment</Comment> 
  <screenShot>scriptsAndAssets/Screenshots/Save1.jpg</screenShot> 
  <MissionFile>scriptsAndAssets/data/missions/wm_SorcerorsIsle.mis</MissionFile> 
  <type>RPG</type> 
  <Game>Trail of stars</Game> 
  <Player>Otto Jax</Player> 
  <CrossbowReloadSound /> 
  </SaveFileInfo>

If I don't assign it, then I still get GameTime...

new SimObject(SaveFileInfo)
{
   GameTime = 0;
};

function UpdateSaveFileInfo(%Comment,%Screenshot)
{
   SaveFileInfo.Location = MissionInfo.name;
   SaveFileInfo.Comment = %Comment;
   SaveFileInfo.Screenshot = %Screenshot;  
   SaveFileInfo.GameTime = 0;   // able to get the field if I don't add $Sim::Time
   SaveFileInfo.MissionFile = $Server::MissionFile;
   SaveFileInfo.Game = $Server::GameType;
   SaveFileInfo.Type = $Server::MissionType;
   SaveFileInfo.Player = $pref::Player::Name;
   SaveFileInfo.ServerType = $Server::ServerType;
}

The correct XML is output if I do not reassign GameTime.

- <SaveFileInfo>
  <MissionFile>scriptsAndAssets/data/missions/wm_SorcerorsIsle.mis</MissionFile> 
  <type>RPG</type> 
  <Game>Trail of stars</Game> 
  <GameTime>0</GameTime> 
  <Player>Otto Jax</Player> 
  <ServerType>SinglePlayer</ServerType> 
  <Location>Sorcerors Isle</Location> 
  <Comment>comment</Comment> 
  <screenShot>scriptsAndAssets/Screenshots/Save1.jpg</screenShot> 
  </SaveFileInfo>

Function that writes out a simobject to an already open XML doc:

function WriteSimObject(%Xml, %object)
{
   %ClassName = %object.getName();
   %Xml.writeClassBegin(%ClassName);
   
   // write dynamic fields   
   %fldcnt = %object.getDynamicFieldCount();
   for (%i=0;%i<%fldcnt;%i++)
   {
      %fldname  = %object.getDynamicField(%i);
      %fldvalue = %object.getFieldValue(%fldname);
      if (isObject(%fldvalue))
      {
         WriteSimObject(%Xml,%fldvalue);
      }
      else
      {
         %Xml.writeField(%fldname,%fldvalue);
      }
   }
   %Xml.writeClassEnd();
}