Time Machine keeps asking to create new backup?
This will not get fixed until Time Machine re-engineer its approach and move away from using a remote-mounted disk image over the network.

The problem lies due to network connections inherently being unreliable (more so wireless networks). However the file system (HFS+) was built for locally-attached disk and assumes that the connection is mostly reliable. Using Time Machine over the network is like writing to a hard drive in which you often unplug the cable mid-transfer. Eventually corruptions occur.

The only way to correct this is to file a bug report to increase the priority of fixing this within Apple's engineering group.

More information here.