Text jumps up and down when editing procedures

When I delete or paste a line in a procedure, the text jumps up or down about four lines every time. It’s most disconcerting and it’s easy to lose your place. Does anybody else experience this?

Wow, I’ve sure never seen that.

I think I need a new Mac or a clean install.


Any text replacing tools in use? (from the OS X Edit menu or in TextExpander)

Any function or workflow associated to the delete key?
(System Preferences > Keyboard or with Keyboard Maestro or QuickKeys)

None of these but the phenomenon is variable so, next time it crops up, I’ll shut down apps one by one and see if I can identify the cause.

But wait - I do have TypeIt4Me but it’s always running. I just quit it and it makes no difference.