Why cant I use 'visibility -> shrink' on some polygroups ?

[system]

Im a relative newcomer to Zbrush having only played around with it a little.
Im attempting some hard surface modelling.

A)In the above image, when I select the purple poly group, I can use visibly to shrink and grow the selection with no issues.
B)When I select the fingers/green poly group and attempt to alter visibility it does nothing ?

What is the difference with the fingers ??

Thanks

Attachments

[Altea]

No welded? If you have used panel loops is possible that the geometry has been segmented in two different islands.

[system]

Thanks a lot… after really fine examination I can see my mesh was separated.
Here’s a pic if anyone else is interested in the future.