Looks like you stumbled onto a sizing bug. What do you have your dialog font set to (Tools > Options > Appearance > Fonts > Dialog). You might want to reduce the point size it if you have changed it to something very large, temporarily so that you can explore all those options, at least.
If you have not changed the dialog font within SlickEdit yourself, then this might be due to a Windows font scaling issue. What settings are you using for?
1) Windows > Settings > System > Display > Scaling
2) Windows > Settings > System > Display > Advanced Display Options > Set a Custom Scaling Factor
3) Windows > Settings > System > Display > Advanced Display Options > Change text size > (did you change any of these?)
I experimented with numerous combinations of these settings and was not able to reproduce the resizing issue you are having.