There is ann issue with undo/redo due to the fact you consider cursor movements as operations to undo/redo:

if I delete a line, then I do "undo", after i move the cursor the redo then fails (due to the cursor movement after the undo)

This happened many times in the past, but now I've understood the reason

Could you please add an option to consider for undo/redo only the operations causing text changes?

Thank you,
Tom

As of PhpED v5.2, all the issues with REDO+OptimalFill+KeepTrailing blanks are completely resolved.
No problems are there anymore.