If I try to save a page like

|{pageflag:key=cleanup_index_home_on_index2.hkg}|blah|blah|

Confluence will complain about the label.

1. For some reason it only complains on subsequent edits, not the first save.
2. The error text says

The labels you have entered contain invalid characters (:, @, /, %, \, &, !, |, #, $, *, ;, ~, [, ], (, ), {, }, <, >).
Label names and prefixes must be less than 255 characters. 

Dot is not in that list, but it seems it should be.

Similar to CONF-6008, but suggest the scope of this bug is just to fix the error text until CONF-6008 is done.