Separate Membership Payment option not working properly

When configuring a contribution page for memberships, the following help text is available for the Display Membership Fee field:
"When this box is checked, the membership fee is included in the listing of each membership option on the signup and renewal page. This is recommended for most configurations.
"If the page is configured with 'Separate Membership Payment' enabled - then just the fee amount is displayed:
" General Membership - $100.00
"If the page 'Separate Membership Payment' is NOT enabled AND the Contribution Amount is enabled so that user's can opt to give more than the minimum membership fee - then the display looks like this:
" General Membership (contribute at least $100.00 to be eligible for this membership)"

On a page with contribution fields in addition to Membership fields (at least when a membership is required), no combination of Display Membership Fee and Separate Membership Payment produces a display of General Membership - $100.00.

The data in the db for is_separate_payment shows 1, so it is unclear why the following in CRM/Contribute/Form/Contribution/MembershipBlock.tpl always displays the second and not the first form of data:

{if ($membershipBlock.display_min_fee AND $context EQ "makeContribution") AND $row.minimum_fee GT 0 } {if $is_separate_payment OR ! $form.amount.label}

• {$row.minimum_fee|crmMoney} {else}
  {ts 1=$row.minimum_fee|crmMoney}

  (contribute at least %1 to be eligible for this membership)

  {/ts} {/if}

I imagine that $is_separate_payment gets messed up somewhere.