I lose my sculpt every time I re-open the project

I’m making a womp rat, and I’ve done the sculpt on it three times now. Next time will be the fourth, but now I’ve discovered that it actually deletes the entire sculpt progress every time I close Blender, or open another .blend file, or just re-open it.
This is with the multi-res modifier, and it gets reset to the default subdivided look. I’m using Blender 2.72b. Is this a bug, or is there something I don’t know about this modifier?

Start a new blend file.
Sculpt something
Show us a screenshot of the full blender interface
Save your blend file
Open the blend file
Show us a screenshot of the full blender interface showing the missing sculpting
Post a link to that re-opened blend file

It seems to save the sculpt information on a fresh blend file, on the default cube.

However, it does not save it in my current project.

Before:


Sculpted:


After saving and opening it again:


Blend-file:
(I am not allowed to post more than three attachments, nor allowed to post links, being a new user here. If you don’t mind, I’ll post an attachment to the blend file in the next post.)

Here’s the blend file: Womp rat 2.blend (1.65 MB)

Delete the multires modifier then add a new one

One other thing with your blend file. At the top of the blender interface you have set the Cycles Render engine but your model is using a Blender Render node material. Materials for the different renderers are not compatible so use a correct material for the renderer you have set

Ah, thank you. Yes, using a new modifier seems to work. I guess it’s safe to assume it was a bug then. I hope it won’t break again…!