QGIS » QGIS Application

I am generating an atlas. For the various sheets, I need to have a textbox in different places - either the left or right lower corner of the map. So, on the layer that defines the atlas sheets, I have added a field legx to contain the xvalue for the textbox position. When I try to use this, it works for a little while, then the textbox disappears from the map. If I look at Position and size, the x-value has been set to 10000000 and is stuck there. Even if I deactiate the calculation on the field or makes a formula that just return a number, the position stays at 10000000. If I manually changes it, it will jump back to 10e6 as soon as I go to another field.
Also, no matter what I type in, I get it set into an expression "coalesce(scale_linear(10.0, 10, 200, 1, 10), 0)" (This is the case when I set the initial expression to 10.0) but with that mapping applied, I cannot see why I do not get 1 returned.

I did fiddle a bit with the tranformation values, but I cannot remember if the problem turned up before or after this.