The Greek question mark ";" should behave as its counterpart in Latin layouts: omit the space before and capitalise next word.
We have started working on this issue and we intend to make a solution available soon. Thank you for your suggestion and keep watching this space for updates.
Kostas Kavourakis commented
This is still an issue in the new SwiftKey 3.0 and it's very annoying.
Not fixed in new version. Shame...