Smarty changes in v10?

I was getting ready to finally deploy v10.0.3 Pro On Site when I found yet another bug in my customizations.

In PDF manager I have some templates that depend on checkboxes on the record.

For example something like:

{if $fields.mycheckbox_c} True {else} False {/if}

This works just fine up to v9.x but breaks in v10 and never prints the "True" part of the statement regardless of the checkbox value.

The default is checked, so there are no "Null" values in that field, they are all 0 or 1 (unchecking the checkbox sets it to 0)

I also tried all of the following without success

{if $fields.mycheckbox_c eq 1}

{if $fields.mycheckbox_c eq '1'}

{if $fields.mycheckbox_c == 1}

{if $fields.mycheckbox_c == '1'}


What changed in v10?

What is the correct smarty way to check if a checkbox is checked (say that three times fast! ;) ) in v10?