Flags with words count disappear

In the user profile we can see the flags with the known words counts. Sometimes they disappear if I do not learn any language during some last days.
It adds the flag again with the correct number when I switch to the language which flag was hidden. But this flag is hidden again when I switch to another language.
Why it happens and what for?

@Ress - I wonder if you can crate a few LingQs in the languages that don’t show to see if they appear there when you then move back to another language.