Hi 
Branches only become stable when that 3rd digit gets to around 3 or 4.
So 4.2.1 is not quite stable branch. 4.2.4 will be. 4.1.5 is stable
branch and 4.0.6 definitely is. When annonucements, marketing-team or
anyone says that 4.2.1 is "more stable" they are not comparing it to
the stable branch, instead they are comparing it to the 4.2.0 (the
older release in the same branch).
However while a branch has not quite reached a stable release it has
tons more devs working on it so it would be a really good idea for you
to post a bug-report about this and any other issues you find;
https://wiki.documentfoundation.org/BugReport
At roughly the same time it would be ideal if you could reinstall
4.0.6 or 4.1.5 and settle on one which does do the things you want.
Regards from
Tom 