$ tpage  tt2-defined-bug.txt

group    1
g        1
group.0  1
group.1  1
no bug

$ cat tt2-defined-bug.txt
[%#
tpage --compile_dir=goner tt2-defined-bug.txt

-%]
[% group= ["one","two"]; g = group.1 %]
group   [% IF group.defined     %] 1 [% ELSE %] 0 [% END %]
g       [% IF g.defined         %] 1 [% ELSE %] 0 [% END %]
group.0 [% IF group.0.defined   %] 1 [% ELSE %] 0 [% END %]
group.1 [% IF group.1.defined   %] 1 [% ELSE %] 0 [% END %]
[% IF g.defined != group.1.defined %]Seems like a bug! [% ELSE %]no bug[% END %]