I use the latest version of the Transmission BT client, 1.61 from memory, on Mac OS X.
I like it but one bug is annoying and requires manually fixing some downloads after a completion.
There are updating torrents used e.g. for distributing software updates that this client doesn't handle well.
Suppose in the first version of a torrent T there's a file F of size 1MB.
I download this torrent and fetch a file.
Then the other day the software gets updated, a new torrent (replacing) torrent gets posted, and this version of torrent changes the contents and size of file F to say 512KB.
I remove the old torrent, add a new one, and start the download.
The current version will put the right contents into the first 512KB of file F but forget to truncate the size to 512KB.
This is especially annoying with configuration text files where it can break a file's syntax.
Also, the client doesn't seem to create empty files specified in a torrent, but that's another bug.