Please refer screenshots below.
Multi-Select is an optional mode at pressent. You have to click that Select button as in left lower part of your pic to quit this mode.
By the way, what do you use Multi-select for mostly? We have a plan to optmize drag n drop with more clear Merge, Child, Link distinction. Which one do you need most?
I select multiple cards mainly to rearrange my mindmap. It would be nice if the multi-select menu disappeared automatically if I click in a blank space. Currently I have to manually close it again and again.