Odd things start to happen after correcting a word and undo/redo

[Reinmar]

Sometimes it replaces the wrong letters. Sometimes it crashes completely (nodelist-out-of-bounds error). Sometimes you get this:

[scofalik]

It's weird because these are just normal operations that works with undo as any other operations. Maybe something breaks when there is insert and remove/move in one batch?

EDIT: Seems like spellchecker generates "empty" insert operation: Applying InsertOperation( 2 ): # -> main [ 0, 17 ]