So, it is a problem of Jahshaka app or was added by SourceForge?
Since the file you downloaded was 178 MB (which is over the VirusTotal upload limit of 128 MB) you couldn't check it there and none of the a/v vendors on VT could know about your program being malicious (which is the point of VT); you are lucky Avast did catch it. Not all of them will.
It has been known to happen an update comes in not put in place by the author/vendor; spoofed as it were. SourceForge has had some issues in the past but then again so have reputable vendor websites.
Be careful what you install on your machine and always prepare for disaster.