0. Set auto-save frequency to 1 minute (for faster reproduction);
1. Open user profile's backup directory (e.g., on Windows it's C:\Users\<username>\AppData\Roaming\LibreOffice\4\user\backup) in a file manager to see its changing content;
2. Create a new spreadsheet; save it as XLS (97-2003) with a password (e.g., as "pwd_backup_proliferation.xls");
3. Make an edit to mark it modified;
4. Wait 1 minute and let auto-save to trigger.
In the backup directory, empty (0-byte) files start to appear ~every 5-10 s, named like this: pwd_backup_proliferation.xls_0.ods; pwd_backup_proliferation.xls_1.ods, ... etc. Closing the file does not remove the generated files.
The impact is not only proliferation of empty files in the directory, but also backup save not working for password-protected XLS files.
Reproducible with Version: 126.96.36.199
Build ID: 62ad5818884a2fc2e5780dd45466868d41009ec0
(there files were named slightly differently: pwd_backup_proliferation.xls_0ods)
and with Version: 188.8.131.52 (x64)
Build ID: 9ba025bafb03b962c34687cf87806cc03a3a7436
CPU threads: 12; OS: Windows 10.0; UI render: GL; VCL: win;
Locale: ru-RU (ru_RU); UI-Language: en-US
In Version: 184.108.40.206
Build ID: 05dceb5d363845f2cf968344d7adab8dcfb2ba71
it works OK: it creates a single file ~10 KB. Closing the file removes the backup.
Just tested to also affect DOC format.
... and with XLSX. Looks like common problem for all (?) foreign formats.
The problem seems to be in ZipPackage::setPropertyValue, where it expects "PackageSHA256UTF8EncryptionKey" or "PackageSHA1UTF8EncryptionKey", but actually gets "OOXPassword" (for XLSX) or "STD97EncryptionKey"/"STD97UniqueID" pair (for XLS).
The debug output lists these lines for each attempt:
> warn:sfx.doc:16096:17588:sfx2/source/doc/docfile.cxx:881: It must be possible to set a common password for the storage
> warn:sfx.doc:16096:17588:sfx2/source/doc/objstor.cxx:1378: Setting of common encryption key failed!
Looks like a dupe of bug 118639
*** This bug has been marked as a duplicate of bug 118639 ***