Please note that this property returns different versionstrings for MariaDB instances on LINUX and WINDOWS environments.
For a MariaDB instance 10.0.17:
on LINUX, this returns strings like "10.0.17-MariaDB-log"
on WINDOWS environments, this returns strings like "5.5.5-10.0.17-MariaDB-log"
To avoid this extra "5.5.5" on windows environments, you could use the SQL query "select version();" rather than this property of the mysqli extension