(Found the problem and fixed it.)
In some script sequences (can send code if necessary) the routine to set the default link in pgsql.c deletes the link before setting it - specifically, if a script issues multiple opens of the same connection string through an included file only.

php_pgsql_set_default_link has a check if PGG(default_link)!=-1. If true, then it does zend_list_delete of old default link and sets new one. If the old default link and new are the same, this sometimes sets the default to an invalid link.

Code should be :
if (PGG(default_link)!=-1) {
  if (PGG(default_link)==id) return;
...

Compiled it, and the problem is fixed. Checked postgresql connections, and they aren't multiplying.