I feel that this must be something to do with Windows. DSLstats saves its window size and position on shutdown, and restores these values the next time it's started. The implementation of this hasn't changed since the early days of the program. You can see the saved values in dslstats.ini, in the section headed "[position]" (the values are in pixels). So it seems that something is overriding the values saved by the program.
[Edit] Just an afterthought - looking at the image you posted above, snadge, it appears that DSLstats is maximised (if I understand the buttons at the top right correctly), so I wonder if clicking on the Restore button would restore the program to its saved size and position.