BUG - Preview the Template blank page

Hi CEd,
on PHP 7.1.6 MySQLi 5.6.23-cll-lve: Joomla 3.7.3, (I updated from 3.4.2) Template Creator CK 3.6.10:
- I opened my old template
- made just 2 info changes
- Actions > Preview: OK > Preview the Template: open a blank page - this happen with site online and/or offline

Anyway, I downloaded my old template modified, installed, ...and have no problems.
Seem something related with the Preview Action... a Bug ?!?

Hi
instead of the preview, use the copy/apply the changes. I have to check this
CEd