A problem with Keep unselected files in "unwanted" folder option

[HanabishiRecca]

qBittorrent & operating system versions

qBittorrent: 5.0.2 / git master (f022ce8)
Operating system: Windows 11 Pro 22H2 / Linux
Qt: 6.7.3 / 6.8.0
libtorrent-rasterbar: 2.0.11+git4b4003d0fd / 2.0.10

What is the problem?

In certain conditions, Keep unselected files in "unwanted" folder option causes massive disk and CPU strain, and also massive memory leak. The effect is very pronounced on torrents with large amount of files.

It appears to be a libtorrent 2.0 bug, qB builds with libtorrent 1.2 does not seem to be affected.

Steps to reproduce

1. Enable Keep unselected files in "unwanted" folder option.
2. Get a torrent with large amount of files, open it in qB.
3. While in the Add torrent window, on the file selector panel, unselect everything.
4. Start the torrent.

Additional context

Despite everything pointing to it being a libtorrent 2.0 problem, I didn't find the root cause yet. But as it directly affects qBittorrent, I opened the issue here for now.

Some screenshots

Windows

Linux

Example torrent: example.zip

Log(s) & preferences file(s)

Nothing in the logs.