To reproduce bug do: past only embed object into the custom tag (without text).
Save object. The embed object is in your tag. Click edit, then click publish - the embed object disapeared from your custom tag.

Suggest patch:

— a/extension/ezoe/ezxmltext/handlers/input/ezoexmlinput.php
+++ b/extension/ezoe/ezxmltext/handlers/input/ezoexmlinput.php
@@ -1339,7 +1339,7 @@ class eZOEXMLInput extends eZXMLInputHandler
$output .= '<img src="' . $imageUrl . '" class="ezoeItemCustomTag ' . $name .
'" type="custom"' . $customAttributePart . $styleString . ' />';
}

• else if ( $tag->textContent === '' )
  + else if ( $tag->textContent === '' && count($tag->childNodes) === 0)
  {
  // for empty custom tag, just put a paragraph with the name
  // of the custom tag in to handle it in the rich text editor