It's been a few days since I updated this issue. OK, so I am having this same behavior on seven separate server installations. We've just completed an upgrade from Ubuntu 16.04 to 18.03 and clean install of php 7.3. Phalcon was built from scratch using these commands:
git clone --branch v3.4.3 --depth=1 "git://github.com/phalcon/cphalcon.git"
./install --phpize /usr/bin/phpize7.3 --php-config /usr/bin/php-config7.3
I did a find / -type f -iname "phalcon.so" and there were three copies of phalcon.so found:
-rwxr-xr-x 1 root root 5312960 Jul 4 00:48 /usr/lib/php/20180731/phalcon.so
-rwxr-xr-x 1 root root 5312960 Jul 4 00:48 /usr/local/lib/php7.3/cphalcon/build/php7/64bits/modules/phalcon.so
-rwxr-xr-x 1 root root 5312960 Jul 4 00:48 /usr/local/lib/php7.3/cphalcon/build/php7/64bits/.libs/phalcon.so
When I built Phalcon, this was the version/date info provided:
PHP Api Version: 20180731
Zend Module Api No: 20180731
Zend Extension Api No: 320180731
And then at the end of the build:
Installing shared extensions: /usr/lib/php/20180731/
Installing header files: /usr/include/php/20180731/
So I'm at a loss to explain what's going on. I've replicated the problem across 7 servers running four different applications with the same results.
It's not the end of the world, but it is confusing and I know that it caused me to doubt that the original update had worked correctly, causing me to spend a few extra hours scratching my head.