WHAT ACTUALLY HAPPENS WHEN YOU DOUBLE CLICK IT, OR A SHORT CUT TO IT?
When I run my program not from a command line, IE is instructed to open the file. This is OK. What is not the expected behavior is that the script interpreter (perl.exe) WAITS for IE to close, leaving it as a console window, a button in the task bar and related things. I.e. it does not seem to be asyncroneous.
On the other hand, I neither expected that perl.exe didn't wait when IE was already open, even if I use system() in the standard way.
The start /B trick with system() was the best workaround in my case. Now, my script always finishes while IE (or the default browser) is loading the html report.