I install updates to my langpack by DnD the .xpi file on fx. After click on "Install Now", I select the "About ..." in context menu of newly install add-on in the Installation tab, and I get description of old version. Note that xpinstall window doesn't show these information too. Maybe it would cause security problems.
I don't believe this is a security issue. Does the correct info display after a restart? If so, this is the same as bug 340219
Yes, it's a DUP of 340219.