While opening a gate valve at the Y mid station we believe that an isolated ion pump volume (~1 liter at a few torr) was released into the tube. Pressure in the tube came to the 10^-6 torr range but is back on the way down. Pressure is currently 1^-7 torr at the mid station and 1^-6 at the end station as the gas sloshes about. The pumping is from the Mid station.
Note that this is not a leak.