You should use -elide option on tags, not '-hidden'.
Look (Win32 command line):

perl -MTk -we "for(tkinit->Text->pack){$_->tagConfigure('hidd',-elide=
+>1);$_->insert('end','x'x45,'','yyy','hidd');$_->update;sleep 1;$_->t
+agConfigure('hidd',-elide=>0);}MainLoop"
[download]

or even

perl -MTcl::Tk=:perlTk -we "for(tkinit->Text->pack){$_->tagConfigure('
+hidd',-elide=>1);$_->insert('end','x'x45,'','yyy','hidd');update;slee
+p 1;$_->tagConfigure('hidd',-elide=>0);}MainLoop"
[download]

Courage, the Cowardly Dog
things, I do for love to perl...