[GNC] Editable and Non-Editable Transactions in the same register

[Mark at Lorimark]

I'm curious what causes register entries to go read-only?

I have an "income" account, where I post invoices.  Some of the entries 
there are editable, and some are not.  I'm wondering what causes these 
entries to be read-only or read-write?

The ones that are read-write seem to be entries that I made manually... 
to 'add bonus payments' to invoices - like adding a 'tip' to a bill. 
The invoice is $100 and the 'bonus payment' is $20, so I went back and 
"somehow I guess" added the additional $20.  Today, I just 'unpost' the 
invoice and add the necessary lines to change the value, re-post it, and 
then pay it (not sure if that's the 'right' way).

The ones that are read-only seem to be entries that came directly from 
the posted invoice.

So, I'm wondering what is controlling the editable-status of those entries?

~mark