Fix#1:: present confirmation dialog, and for this software, I wouldn't give the user of turning if off, because deleting transactions isn't so common, so user really doesn't need to be able to switch it off, it's better for him if he can't!!
(2) ....<snip>..... when you edit an existing transaction, when you press 'Save to Db', you get a nice yellow confirmation, but then everything stays the same! In one way I can see the logic of this, because it is not like entering a new transaction, after editing an existing one, you aren't so likely to be start entering a new one right away. .... <snip>... And there is a bigger problem with this. If you press 'Save to Db' again, the transaction gets entered again - you now have a duplicate transaction! The first time I did this, by accident, luckily I noticed the duplicate transaction, otherwise it would have skewed all my expenses for that month, without me realising.
(3) Sorting in the 'Expenses' view. ....<snip>
....<snip>....I know you have made a manual for this software, and maybe I am guilty of not having read it, but really, with a software like this, there should be no need for a manual that the user has to read. It should all be pretty self-evident, I think.