Alt+up/down broken in code editor

Alt+Up/Down keys allow quick functions browsing in code editor, but oddly this is broken on the 3rd tab of my 5 tabs project, where alt+up/down won't go below the 2nd function (all other tabs are fine). Have no idea why, I even got rid of all my code & data to see whether this comes from that. This is the cart joined here: no data, only function names & some comments, but in tab 3 alt+down won't go under the parts_add function.