It's possible to switch off the setting "Enable at start", but I wish I could switch off "Disable on exit" too. Whenever I exit Locus, I get a popup saying "GPS disabled". Well, it's impossible to toggle GPS in Android 2.3+, and I wouldn't want Locus to disable GPS anyway.
It actually doesn't toggle off your devices GPS. It is just a simple notification which tells you, that Locus doesn't use your devices GPS anymore.
I'd also like to see this removed! It's VERY annoying when going in and out of the app. I believe Menion said it's a bug and will fix it soon.
hmm this "bug" is already fixed. If you don't want to disable GPS (in Locus not in system as Matthias correctly mentioned) when you hide or minimize Locus, just disable it in settings ...