1. Open SCAYT sample at https://www.webspellchecker.net/samples/scayt-ckeditor-plugin.html 2. Disable spell checker first 3. Keep cursor at end of a correct word and press I (italic) button or use CTRL+I to apply italic style 4. Write some characters to make the word invalid. 5. Turn on the spell checker 6. Now press undo button or use Ctrl+Z to undo the writing of text. After step 6, undoing once has no effect. It works if undo button or Ctrl+Z is pressed 2 times fast. Please see attached video: [2017-09-08_1319.zip](https://github.com/WebSpellChecker/ckeditor-plugin-scayt/files/1287448/2017-09-08_1319.zip) **NOTE:** If SCAYT is not enabled by default, you need to enable it first, disable it and then perform further test case steps.