I stood 5 glasses upright; one in each corner and one in the middle and periodically checked during the first cycle for water-in-the-glasses....
First test I did without adding any additional water and the glasses in 3 corners and the middle were starting to fill up, by the end of 5 minutes, they were all full except one of the corner ones.
The second test, I added water to just above the heating element, I also checked the over flow float and it was at max height. Anyway after turning on the unit the glasses filled up much faster, probably within a couple of minutes, except again one of the glasses in a corner.
With the first test the pump did sound as if it was cavitating, a sort of pulsing sound, maybe sucking in some air.
Hope you can make something out of this.
The kicker is that we are moving to another house in about a month, but I don't really want to leave this problem with the next residents.