Trying to book flights to/from SFO in April and May, I came across several of the bugs mentioned in this thread, namely:
* nowhere to enter promotional codes (like BACHASE10)
* higher pricing sometimes presented, depending on whether one is logged in or not (or perhaps for other reasons!)
* free seat selection in F
* name, address, credit card info not presented and had to be filled in manually

Workaround:
I found that when I initiate my flight request using flight.google.com, and once flights are selected, follow their link into BA, all is well. I bought one flight this way and will shortly buy another.

PS: I noticed later that Leonidasc mentioned the google flights thing earlier in this thread!