We are using the Lingotek translation service for our Drupal 7 site, and have experienced the following very similar problems.
Case 1: Content types - Monthly Product Update AND Blog post
Server1 - Behaving - Language setting: English (as seen in Content listing) - Enabled for translation: No, then No
Server2 - Misbehaving - Language setting: Language Neutral (as seen in Content listing), changed to English - Enabled for translation: No, then Yes
Server3 - Misbehaving - Language setting: Language Neutral (as seen in Content listing), changed to English - Enabled for translation: No, then Yes
Consistently, for Server2 and Server3, for this Content Type, I enabled Multilingual support, then in the node, changed the Language to English.
The Misbehavior: This node initially displayed all of the content in View mode, but nothing in Edit mode. Changing its multilingual setting AND changing the language to English resulted in the following:
What was previously displayed in the Edit mode (nothing) became the display in the View mode, i.e. nothing. The content was lost entirely.
From another instance of the site, I copied the source for this post and pasted it into the Body field and saved it... The node now displays in both Edit and View mode as expected, and further edits have been reflected appropriately.
Case 2: Content type - Product Page
Server2 - Misbehaving - Language setting: Language Neutral (as seen in Node and Content listing), changed to English - Enabled for translation: Yes
The Misbehavior: Complaint from editor that edits made, additional text added to Body field, are displaying in View mode, but not Edit mode - which I verified.
Aside: I used Node Export to export ALL the code for this node and checked it for the missing content and it was NOT there.
In View mode, I copied the HTML with the edits and pasted it into the Source for the Body field, which made the View and Edit modes sync up. However, I did not change the Language setting at this time.
The following day, the editor complained that her edits were visible in Edit mode, but not in View mode...
This time, since there was nothing else I could think of to do, I copied her source code for safe keeping, and then changed the Language setting from Language neutral to English... this actually reverted the Source/Edit code to match the View code - which did not have the latest edits!
However, now that the Language was set to English, I pasted in the saved Source code and THEN... the Edit and View modes matched up, AND further edits have been reflected appropriately.