Can't save serialized data (loading work) in Playerprefs for WebGL Build.

We are saving data using serialization and playerprefs with a code similar to the one by JCCurrie described here : http://answers.unity3d.com/answers/56595/view.html

The behaviour works well on Mobile, the webplayer and WebGL versions.

We've made a few test with WebGL build and everything was fine.

Then we build the final version of our project in WebGL we changed the "Stripping Level" to "Strip Assemblies" (it was at disabled before) as it is said here : http://docs.unity3d.com/Manual/webgl-building.html

We've then note that the game was still able to load the data, but it wasn't able to save it anymore. (We had no error or warning in the javascript console when the game was saving).

The bug only seems to trigger after we've changed the strip level of data that was created before we changed the strip level. If we change the strip level back the bug is fixed.

My question is why it happen? Is it a bug or it's expected and I'm missing something? Is there a way to make saved data compatible even when you change strip level?

Thanks!