I dont think the problem you experienced was a "bug". you were doing a screen capture, in which case the application name has an ambiguous meaning -- and minicap wasnt capturing it. $appname$ is for when you capture an application window.
Having said that, i've uploaded a new version with some fixes. It now will grab $appname$ as the foreground window name, plus i added a few more options. Let me know if it solves your problems.