While it's not a worldwide issue, but it still annoys a lot of users of one country in the World - Lithuania.
Using Lithuanian keyboard it is impossible to enter numbers 1, 2, 3 and 5 in essential apps like Outlook Mail, Outlook Calendar and Word. When typing these numbers the paragraph styles are changed instead. This issue is applicable to number of previous OS releases and I guess all phones running Windows 10 Mobile.
The problem was communicated via Feedback Hub app, answers.microsoft.com by number of users. However, there is no way MS listens.
[UPDATE: 03-04-2017]
Problem was solved in Outlook Mail and Calendar app version 17.7922.42018.0 and Word app version 17.7870.47742.0. Thank you, Microsoft!