Bubble Tea v1's reader parses input 256 bytes at a time. When a read ends inside an SGR mouse report ("ESC[<64;19;5M"), the ESC [ is taken as an Alt+[ key and the rest arrives as typed runes, so scrolling typed "[<64;19;5M" into the prompt. Trackpad bursts fill the buffer easily. v1.3.10 parses the same way. A program filter turns the Alt+[ and "<b;x;yM" pair back into the mouse event; a lone Alt+[ is dropped (unbound; Option+[ arrives as a character).