If, in TCC v19, I "F1" the help file opens. If I go back to the console and "F1" again, another copy opens. And so on. V18 does it also, but versions of TCC prior to 18 don't. The behavior is the same with or without a command line in progress.
This has been discussed several times previously. Microsoft broke the HtmlHelp API in recent versions of the SDK when running Windows 10, so I had to drop the call & execute TCMD.CHM as a separate process. (Microsoft's response thus far has been that .CHM files are obsolete.)
The only ways around it are (1) use an old SDK and drop Windows 8 & 10 support (not likely to be popular with the users), or (2) use the separate process.