When importing QFX, what does 'U+R' actually do?

[George Riner]

I'm downloading transactions from my bank as QFX file. I then do a 
File->Import, select my downloaded file, and then it opens the 'Generic 
import transaction matcher' and does the 'bayesian matching' on 
transactions downloaded to matched transactions in the account. The 
choices of actions to take are the 'A', 'U+R', and 'R'. I get it that 
'A' is to have the downloaded transaction added to the account. I also 
get that 'R' is to mark the matching transaction in the account as 'c' 
in the R column. But I don't get what 'U+R' is doing. I take is that it 
means doing the 'R' part and marking the matching transaction in the 
account with a 'c' in the R column, but just what is the 'update' part 
of 'U+R' updating? The comment to the right of the downloaded 
transaction in the transaction matcher says: 'Update and reconcile 
(auto) match'. What is being 'updated' to the matching transaction?

Using Windows 10 (64-bit)
GnuCash v. 2.6.13

:George
Sebastopol