Hi ,
1st Issue
I found that if I give fields a default value, the problem goes away. However, if I simply do as you say and enter it into the default web app before saving the page, it still won't save. I can see where I may run into future issues with this since you can't have a default value for a user/group field.
2nd Issue
I was able to get it to work with your example, but a key hurdle was that I had the field set as a lookup field. I deleted that and recreated with a normal text field and it started to work.
Thanks