Given the fact that the downloads for the Linux version and the portable Windows version don't even have a license file (or a readme, or anything really), I'd assume it isn't open source. The linux zip file just contains an executable file and the Windows portable version has an exe and a few dlls. Pretty safe to say that it is free/gratis, or donation-ware to be a little more accurate, but not free open source.
Having tested out Feng Office, I'd have to agree with you. The big list of features not available in the community edition was already a stumbling block, but the vague "You don't have permission to access requested page" message that I got while logged into as a Super Administrator was just silly. Yes, I was trying to access a feature not in the "Community Edition" (Mass Mailings), but, at best, it should have failed in a more understandable manner than "you don't have permission". Overall, I really like Feng Office, the software is really nicely designed, but their paid vs. community distribution method is a huge turn off.
Given the fact that the downloads for the Linux version and the portable Windows version don't even have a license file (or a readme, or anything really), I'd assume it isn't open source. The linux zip file just contains an executable file and the Windows portable version has an exe and a few dlls. Pretty safe to say that it is free/gratis, or donation-ware to be a little more accurate, but not free open source.