**System Information**
Arch x64
**Blender Version**
Broken: Blender 2.69 r95d3286
**Short description of error**
In a newly opened .blend file, Multires modifiers appear to lazily load external displacement files if the viewport level is 0 or viewport visibility is disabled, then load them if those settings are changed or if sculpt mode is entered. However, if edit mode is entered on a mesh before its .btx displacements are loaded, the displacements appear to be lost when multires is next enabled, and definitely **will** be lost if the .blend is saved once this happens
AFAICT this does not occur with regular "packed" displacements, nor with .btx files that have been loaded prior to entering edit mode
**Exact steps for others to reproduce the error**
1. start with any mesh
2. add multires and subdivide a few times
3. enter sculpt mode and do some sculpting
4. exit sculpt mode
5. use multires' Save External and save the .btx
6. set either multires' preview level to 0, or disable its viewport visibility
7. save and close blender
8. reopen the .blend file.
9. before touching multires, toggle edit mode
10. reverse what you did for step 6
11. displacements have not loaded. inspecting the .btx file in a hex editor implies the displacements are still intact
12. save. inspecting the .btx file again, the displacements have been zero'd out
the attached .blend is ready to go at step 8, and has viewport visiblity for multires disabled