I can confirm your first notice and your second warning.
But I do not have your third warning ("Cannot modify header information...."), and I do not have a blank page, but the correct page is displayed (the page with the new question).
(I use display_errors = Off, and log_errors=On in my php.ini).
These log entries do not seem to be "errors", but just "warnings" about a null value at runtime..... (that I can find correctly -in my opinion- in the qa_posts table, "tags" column, when the question is inserted)
I think that checking the value of the array/variable with an "isset" these warnings will disappear....
But I'm not a php expert