Second register shows outstanding stuff (7)
I believe the answer is:
backlog
'outstanding stuff' is the definition.
The definition and answer can be both related to property as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'second register' is the wordplay.
'second' becomes 'back' (to second a motion is to back it).
'register' becomes 'log' (a log is a register).
'back'+'log'='BACKLOG'
'shows' acts as a link.
Can you help me to learn more?
(Other definitions for backlog that I've seen before include "work not yet completed" , "Work still undone" , "Amount of uncompleted work" , "Pile-up of work still to be done" , "An arrear as of work" .)