Ditto.

On what basis did B protest?  How did boat A infringe boat B?

If A is to windward of B and they have to make the mark then surely B has to tack as well. It would only be a matter of seconds before B tacks.

I think the question is does A have the right to tack or can B take A past the mark?

In which case, A would be at fault if it had caused B to take avoiding action.

Yes, but so what?

Note this is still the A to Windward scenario. 

As long as A is to windward, A can tack at any time, subject only to B not having become overlapped to leeward and being hooked up so tight on her leeward quarter that A cannot change course without B needing to take avoiding action as A's stern swings.  If B does need to take avoiding action, A simply breaks rule 11.  Mark-room does not help A, because although A is entitled to mark-room up until she passes head to wind, her mark-room does NOT include room to tack, because she is the windward OUTSIDE boat, not the windward INSIDE boat (Definition mark-room).  Yes, B can take A outside the mark if B is good enough, but remember that B's lee quarter hook-up, going upwind, is about as slow a tactical position, relative to A, as it is possible to find, and it won't last long.

If, in the shifty conditions, A has sagged down to clear ahead right on B's line or to leeward of B, then A's mark-room still does not give her room to tack, because if she is clear ahead straight ahead of B, she is is neither windward nor leeward, nor inside nor outside, and if she is to leeward, she is not the windward boat.  From anywhere in the clear ahead or leeward berths, A may begin to tack, changing course towards the wind, but subject to rule 16, but once she passes head to wind, rule 18 ceases to apply and rule 13, then rule 10 apply so that A must keep clear of B, thus, once A has passed head to wind, if it is necessary for B to take avoiding action, then A has broken rule 13 or rule 10 (depending on whether A has reached a close hauled course or not).