Currently what happens if you copy&paste some cells from a table (either from within another confluence table or from external sources like Excel) is often unpredictable and seems to be dependent on the browser used (Firefox 9 vs. IE ), the source and some other conditions unknown to me, because it varies from time to time and PC to PC.
This is clearly not acceptable. Tabular data from any internal and external source must be treated equally and in a way the user can influence.
I every office suite I know there is this "Paste as ..." action where the user can choose how to cope with the content in the clipboard. I believe it is time that Confluence also explicitly asks the user how he wants to to insert tabular data from the clipboard
- either "overwrite existing table data"
(possibly asking the user if the existing table is to be extended if it is too small for the content to fit in, otherwise truncating the content in a sensible way retaining the correct columns below each other)
- or "insert into a table" that is, inserting as new rows into the existing table, possibly with some empty columns
- or "insert as table", that is, add it as a separate table within one table cell if applies
IMHO "overwriting existing table data" should be the default behaviour.