Thank you Hilary,
Luckily this problem is now solved and I get to familiarize myself with logic inspector :)
Of course, checking the rules there shouldn't matter since pressing the button doesn't execute but submit thru main connection. Anyhow the problem is in database functionality which adds blank spaces in the end of field values and therefore the value changes in the form (and in my case triggered whole lot of rules). It's funny though that even though the values in the database get blank spaces, those blank spaces are not forwarded thru email submitting (even though the email submit rule is after database submitting).
Long story short, I think the form sends different values to database (eg. "FI ") and different values to email receiver ("FI"). This I consider somewhat confusing.