It seems that case-insensitive regular expressions become case sensitive after a literal '.' in the pattern. Below is a test program compiled with DMC version 8.33 and a sample run. Note that every test string should match but uppercase chars after the '.' cause no match.

**** test program ****
// retest.cpp - RegExp test
// argv[1] is pattern
// search for pattern in argv[2..argc-1]

#include <iostream.h>
#include <regexp.h>
#include <assert.h>

main(int argc, char *argv[])
{
    assert(argc>2);
    RegExp re;
    assert(re.compile(argv[1],"i",1));    // "i" = case insensitive
    for (int j=2; j<argc; ++j) {
        cout << argv[j];
        if (re.test(argv[j]))
            cout << " match " << re.pmatch[0].rm_so << ' ' <<
re.pmatch[0].rm_eo << '\n';
        else
            cout << " no match\n";
    }
}


**** sample run ****
**** (note . after \  in some fonts it is hard to see) ****
C:\dm\temp> retest  a\.b  A.b a.B  A.B  a.b
A.b  match 0 3
a.B  no match
A.B  no match
a.b  match 0 3