Asterix on dates that don’t have constraints?

I understand that activities starts and finishes that are constrained have an asterix next to the date.
I am finding that I am now getting the same asterix on start and finish dates that are not constrained. There doesn’t seem to be any rhyme or reason to it.
Anyone know why?
This is causing problems as PM’s I work with are asking why I have constraints in their schedules.

Help!
Cheers,
Dave