There are already a number of issues on the github: https://github.com/bitcoin/bitcoin/issues?q=is%3Aissue+is%3Aopen+UI+freeze
If you know you want to just look at the wallet and aren't fussed about the syncing, click the little "network" icon in the bottom right corner and it'll instantly disconnect and stop syncing... then you're free to do whatever you like in the wallet without needing to worry about the UI freezing up on you... once you've completed whatever it is that you want to do in the wallet, just click the icon again to reconnect and continue syncing:
Thanks. That's the answer I was looking for.