I have the same problem with Imposer 11.0.9.
I created an .fpi file.
When I re-open it to adjust it, most settings have changed.
Finish Size have gone from 145 x 295 mm to 25.4 x 25.4 mm (1"x1").
Sheet Size was SRA3, but is now Tabloid 11"x17"
Also spacing has changed.