Yep, happens for me too.
I've never noticed that, but then I mainly use Tableau as an analysis tool rather than for presenting data, so don't tend to need to worry about the sorts of things you are doing in building the label there.
It's just a precision/rounding issue with the way the STR() function is implemented with the data engine, I'd say. Worth logging a bug report, though I'd say it must be known by now.
You can work around it with some ugly string expressions - see attached.
April-Mixed Labels RL.twbx.zip 103.6 KB
Some serious ugly indeed! Thanks Richard.