I'm using version 2.4.2 on a Windows 10 machine.
The issue I found was when I change the name of the movie set manually and save the entry, the name of the set is then changed to a combination of the old set and new set.
When I look at the .nfo file, the change appears as follows:
<set> [old name] <name>[old name][new name] </name> </set>
If I change it in Mediaelch again, the problem is compounded. If ABC is the old set name and def is the new set name, the first change looks like this:
<set> ABC <name>ABCdef</name> </set>
The second change looks like
<set> ABCdef <name>ABCdefdef </name> </set>
If I manually change the .nfo to remove the entry in the <set> tag, it seems to be ok.