In my project I use both pcre and poco. Everything was fine before pcre update to version 8.30. Pcre developers did lots of things with utf8 and utf16 support and added functions like pcre_utf8.
Poco foundation libraries even if configured unbundled use "pcre_utf8_objects = pcre_ucd pcre_tables" where names like pcre_utf8 are defined.
So when I link libraries in order "poco pcre" I get error behavior and when link "pcre poco" my program works fine.