render :partial erroring with wrong extension

I'm thinking that for some reason Rails isn't seeing a content_type so
is falling back to .erb rather than using .html.erb, but I can't
figure out how this would happen or why it's not able to find the
correct file. I encountered this when changing this view from <%=
render @gigs %>, which finds gigs/_gig.html.erb just fine. I can post
the contents of _gig_big.html.erb if necessary, but for the most part
it's just a copy of _gig.html.erb (for now).

View:
<table id="gigs" class="smalltype">
  <%= render :partial => 'gig_big', :collection => @gigs %>
</table>

Error:
ActionView::TemplateError (Missing template gigs/_gig_big.erb in view
path app/views) on line #9 of app/views/gigs/index.html.erb:
6: <% end %>
7: </h2>
8: <table id="gigs" class="smalltype">
9: <%= render :partial => 'gig_big', :collection => @gigs %>
10: </table>
11: <% end %>

Partial:
../app/views/gigs/_gig_big.html.erb exists

Of course it was the one thing I didn't check and was not in the
error: a leading space in the partial's filename. A twitchy typo, and
a proportional font didn't help either.