Looks nice. I just clicked around a bit (as I'm not doing often flowcharts in life) and:
; pressing "add node" repeatedly I expected to get them linked one after the other (wrong expectation)
; if I change the type from rectangle to rhombus its center is more on the right breaking the connection lines (bug)
; if I had node1->node2->node3 and I delete node2, I expected node1 to be linked to node3 (wrong expectation)
; after the above action, when I press add node, node3 just disappears (bug)
