I am still using the most up to date version 7 (I have not updated yet) and I am always running into an error which requires me to close down the program to be able to save, a "runtime error". Other than that, it has not been too buggy. Version 8 is new, so perhaps that are working out some kinks. I would contact them, they are really good with responding.
A good system restart always tends to help. I know having a few adobe products open can sometimes mess around with how screenflow works.