I've copy the whole string from your post into the field ("€ 5,45+2,47-3,25") and it works! Iget the correct result € 4,67, as you get.
I catch the error if I don't type a space between the currency and the first digit (for example try exactly this string (without any space after currency): "€5,45+2,47-3,25". What happens?
Furthermore I catch the error if I don't erase the space in the initial empty field between the currency and the first 0 digit. This is exactly the sequence I wrote you in my second post:
If you double click (only one double click) on the amount, the digits will be selected (i.e the red part of the amount in the field "€ 0,00" of a new task; the currency symbol won't be selected, only digits)
Note that the space between the currency and the first digit (in the quoted text) isn't selected after the double click.
Regards
Gualtiero