I think there are 2 points here.
1) When copying a quote you can type in a quote number and click tab to bring up the search screen, however the search screen uses the top most previously entered quoteid to return the lines to copy. If you click enter instead of tab it does the same but also tries to confirm the copying of the quote and throws up windows in the background for mandatory fields.
2) To actually copy a quote you must click on the search option from the Based On drop down type in a quote id and click search, then you need to click to select the quote (as a partial search may return more than one row.) Then you are presented with the lines of the quote you wish to copy (which is expected and ok). This process doesn't seem particularly obvious and a little frustrating.
An ideal experience would be to replace the Based On dropdown component with one that acts like the product search on a standard quote with the look ahead functionality. If this was in place you could almost eliminate the need for 4 or more clicks/enters.