The multiple line past still needs work, as of Git 1.31. Here is what works: <img src="https://cloud.githubusercontent.com/assets/2631430/18294391/1b2bdeb2-7499-11e6-904b-d0b0db5d735d.gif"/>
What I would like to see working - is when you copy some text single line, then select multiple rows in a multi-line select and then paste the copied text into each multi-line row selected.
Instead this is what is happening as of Geany 1.31: 
It would also be useful if you could copy multiple lines of text then select the same number or more lines of text and paste the multi-line text copied into the selected area. This doesn't work either.