I purchased BTSync Pro today with a sense of enthusiasm after reading about the software. I installed the free version but then realised that this didn't give selective sync, so I took the plunge with Pro immediately. But before I moved over hook, line, and sinker from my 7 year relationship with Dropbox, I spent the day testing BTSync. I didn't expect to find any problems, after all it has received glowing praise - and it's the future of sync, right? No, I tested BTSync because I thought I really should make sure I know exactly how it works and behaves in certain scenarios. Dropbox really has been brilliant over the years, it's never given me a headache, it always "just works". I know what complex stuff happens under the bonnet to keep things ticking away like that, having spent many years troubleshooting other sync systems in an enterprise environment, and charting their development for almost 2 decades (yes), such as Microsoft's Offline files, rsync, Synctoy, Pydio, OwnCloud, and more. I have come across numerous bugs with various sync softwares, and banged my head against brick walls for sometimes weeks just to resolve issues with sync technology in a domain-wide environment. So - I thought things had moved on. This is peer-to-peer. Forget the cloud, forget old technologies. This stuff should just work, and fast. Within a day I'd discovered the most basic of bugs. At first I assumed it was me, my understanding of the software, or my settings. After going through each setting individually and testing what effect it had, and testing further, I concluded it wasn't me, it was BTSync. Here's the bug, I'm guessing I'm not alone in noticing this. Install BTSync on two devices (in my case 3) Licence it, to gain the selective sync and device management features Create D:\BTSync on an "always on" server. (That's how I chose to implement it.) On all clients, set the default location. (Settings > My Devices > Default folder location), and set the sync mode to "Synced", not disconnected or selective. Add a Standard Folder. This folder then appears in windows explorer on each client. Create an empty text file on Client #1 Wait for this to sync to Client #2, then on Client #2 add some text Close the file on Client #2 and re-open it. Wait - the text I added and saved has disappeared. This doesn't happen every time. It's intermittent. However in my testing today it happened I'd say 30-50% of the time. Certainly enough to ensure I would NEVER want to use the software in an environment where I might spend hours working on a document and hoping that when I save it, the contents wouldn't be lost. I went through all kinds of testing today from checking the NTFS security permissions on the files to looking at the .sync folder data. Of course, I found that the data I attempted to save was not completely gone - I could retrieve it from .sync\Archive. Thus showing that BTSync had knowledge of the fact I saved it, and this wasn't some random problem caused by another piece of software. Is this a flaw in clock sync or somesuch? Surely BTSync doesn't use the native system clock, which differs from system to system, in order to determine file update times and therefore determine which the latest version of a file is? Please tell me that isn't the case. That would be far too obvious.