I have just installed the latest version of QMC 18.104.22.168 and I am encountering the same problem on an XP SP3 operating system.
It doesn't shut down immediately, but will usually give an error message within 5 mins.
I did manage to test converting a couple of files and was very pleased with the results.
It did not shut down while converting, but shortly after completion or while configuring settings prior to starting conversion.
I am very pleased with what I have seen so far with this product. I hope this item can be resolved.