< Undoable always looks as though I've spelled it wrong.

I know what you mean, I always tend to change the syntax
of the sentence and use 'can't undo' or 'can't be undone'
or some such workaround.

I also seem to have a mental block when reading it, my thought
process usually runs along the lines of ...
Undoble? Hey! What? oh undoable OK. <g

Regards
Martin