You're talking about upwind, right?

It sounds very strange. There's no logical explaination for that, but these things are so hard to describe with words. I bet it's something dead obvious though, which is probably something else other than mast rake.

Raking the mast back would affect the feel of the boat a bit, but obviously by the same amount on both tacks assuming you dropped both shrouds back the same amount.

So, dunno.

This is going by purely what you have said above but if befor ehand you had very light and neutral steering it sounds as if you had the right settings initially, usually you would drop the shroud points for slightly heavier weather and at the same tyime what we ofund in the 200 was that you had heavier steering until you raised the centre board a bit which helps tremendously infact its the same in the 300 by lifting the board up a bit in the white stuff it eases the steering ive found. So give that a try. Could also be a problem with your sail shape perhaps the slot asweell or maybe your spreader lengths and angles are not the same which could possibly give this problem but you would probably see characteristics of this in the mast which you say is straight but it could be worth checking all the same. Did you move the mast heel position also or just drop the pins a bit. An inch sounds like quite a big difference i know that the difference between our light and heavy settings in the 200 are not as much as that but we also move the mast heel position which makes a difference.

The actual construction of the Xenon hull may be causing this effect. We noticed that on the Omega, when the rig loaded up the hull over an extended period of time that indentations in the hull became present within the points near the shrouds. What may have happened is by moving the shroud down one pin, you have increased the loading on the hull to the extent that one of the shrouds is causing the hull to flex on one side when the boat is powered up while the other side is still rigid when loaded up. The Laser Vagos made from the same hull material don't use high rig tensions probably for the reason that the hulls are not rigid enough to support high loads without flexing.

I asked the Topper rep at the Boat Show in January what the main differences were between the Xenon and the Omega...he pointed out the alloy bar running across the Xenon and said something like "that's to stop it folding up like the Omega does when you put lots of rig tension on"....

Could you have the lower shroud tension much more on one side than the other .  They are only done up with bits of string and it is quite easy to do.  If one was very tight, and the other loose this might make it different one side to the other. 

If you tension them before putting on jib tension, it may even make the mast lean to one side regardless of the shroud tension, by twisting the whole rig.

The mast would bend one way on one tack and the other on the other.

It may seem odd, but it works. The classic boat for low rig tension is the Firefly, and the sails are cut to make low rig tension work. Our Firefly is nearly 50, and is still competitive in the fleet. I have my doubts that and Vagos will be racing in 50 years, but the premis is still the same - low rig tension means folding your boat up less, even though windward shrouds go tight.