When you double-click a helix or a sheet in selection interface, the Rebuild button appears. When you then double-click another helix or sheet it disappears again although the new helix (or sheet) is selected and the tweak tool is available. Even the hotkey O is disabled in this case.

Confirmed.
My OS: vista sp2
Bump. Not fixed yet and very annoying.
I select a part (d-click): rebuild pops up, then second part (ctrl+clik): rebuild gone, then 1 another segment: no tool, then deselect last segment: tool is back.
Add on: because we can rebuild even 1 segment rebuild tool should show up just after we select one segment. Sometimes I need to rebuild 2 close loops (not chain of segments but 2 different places)- button should be always accessible.
Yes, tweak tool is acting strange too. Not using it as much as rebuild, but same thing.
Thanks for reminding us about this bug.
Thanks for reminding us about this bug.
Thanks for reminding us about this bug.