This is deliberate. The period separates the radio button option name, "single input," from the label of the text field that comes after it. This would probably be clearer if the spacing were adjusted so that there were more space after the period than after the colon. But, don't hold your breath.
Yeah, Jens is less religious about the exclamation mark than I am. :~)
The difference is that those don't have an extra field, though I do think having a hyphen would be a bit better than a period (even though the period is good enough for me).
That makes the spacing even worse, making "default value" look even more like part of the option text rather than like a label for the text field. If anything it should be
That was actually the first thing I tried, but for some reason it didn't work. Of course I actually also moved the "Default value:" label over to the left a bit.
I have a feeling I know why it's not working, but it's not something that needs to be fixed, seeing as how it's something to do with dev mode, and doesn't effect snap in any way.