So . . the expansion of the mast should negate the expansion of the headstay and backstay, so we're back where we started.
Maybe it comes down to "unaccustomed use."
As others have pointed out, the mainsail provides a lot of support for the mast on the wind, and it's not customary to sail with a lot of jib and no main when going to windward in heavy weather.
I think Neil is doing the right thing by taking a close look at everything.