I'm having this really weird issue at my work. We have a 1TB GoFlex drive formatted as exFAT (originally formatted on Windows 7 machine). This drive is being used on both Mac and Windows. When I'm on my Mac I am using Thunderbolt adapter, when on Windows I use USB3 adapter. Everything works nice until the point when I use the drive on Windows machine and then bring it back to Mac. In OS X (10.9.4) the drive does not get recognized and I have to use Disk Utility to repair it. This is strange behaviour because the drive works flawlessly when it's mounted and we made sure it's not HDD failure. We are also using exFAT formatted USB3 drives that we switch between machines and there are no problems with that. Any ideas?