Deleting files from 7z with old compression makes it a ZSTD archive

[Luashine]

Version: 7-Zip 19.00 ZS v1.4.8 R1 x64 and 7-Zip 21.03 ZS v1.5.0 R2 x64

1. Create a 7z archive with old compression to share with the world
2. Notice a mistake, delete a file/folder inside
3. The archive has now the ZSTD compression method, impossible to open in default 7-Zip (click the INFO icon on the top-right)

Expected: modifying the archive with 7-Zip ZSTD does not introduce new compression algorithms that'd "break" the file for other users.

This seems to be similar to #111 where an archive is modified by drag-and-drop.

PS and Update: in #111 I read that this fork should save the last setting in registry. Instead it should check what compression algorithm is used in the archive and use the same algorithm for operations.

First accident:

Reproduction, original archive:

Same archive after deleting a folder:

[Vangelis66]

Related: #263

[mcmilk]

Can you re-check this with latest pre-release ...

[Luashine]

@mcmilk with latest pre-release (v22.01-v1.5.2-R1).

Severe bug: when I compress files with "LZMA2 [std]" then the resulting archive reports "Method ZSTD:v1.5,l2" - where "l2" is the selected LZMA2 Compression level and Info - Method says "ZSTD". WinRAR cannot extract such an archive, I suppose it's really not the default LZMA2 = its not a display error.

LZMA2 Fast compresses correctly into LZMA2. Other algorithms works correctly, only LZMA2 std does not.

[mcmilk]

Okay, I will re-check this with that provided info.