OneEyed, it's not supposed to re-indent the entire thing when you change it, that's what Ctrl+I is for
I've just released Pawn Studio 0.8.2, this version again fixes a few issues and comes with an improved indentation. From now on it supports custom tab sizes, which can be changed in the Settings dialog (Editor -> Indentation). It can now auto-indent your templates as well, you just need to activate that in the settings.