Symbols remain after running strip

After trial and error, a static commercial release works OK on XP. QtSDK 4.7.3 and its mingw are the basis. Unzipped the commercial tree along side and found an acceptable combination of switches and directives from various messages on the subject.

The final executable is larger than necessary because of leftover symbols. This by itself is a mystery. I presume that a 'release' build should remove them.
Several forum messages suggest running "strip --strip-all <filename>". It seemed to run OK after placing it at the end of build, but the file didn't change. Just to be double-sure, I navigated to the final output folder and ran 'strip' there - still no.

Can anyone explain why the symbols are still present, and then how to remove them? In my experience with other compilers this is the linker's responsibility.

Thanks in advance,
Scott