I've investigated this over the past hour and it seems that this is a side-effect of the Explorer context menu shell extension. Windows uses a dedicated mechanism to load those extensions in memory (a so-called COM Surrogate) which is apparently listed as separate process without icon in the task bar.
This is far from optimal, but I don't know how to circumvent this currently. I tried to see how other programs are dealing with that and the latest preview of WinRAR shows the same behavior.
If anyone knows how to circumvent this, I'm happy about any pointers.