Step to Reproduce
1)Open the attached file. 
2)Select the last slide in slides pane, Tools->spellcheck(or press F7), 
click “yesâ€.You can find the first slide is selected in slides pane, 
click “resume†button in spellcheck dialog box. And pop-up the “spellcheck of 
entire document has been completed†dialog box, and the last slide is selected 
in slides pane. Click “okâ€button , the second slides is selected .
The first mistake is that the first slide  is not spellchecked .
If you click “ignore once†to end, pop up “spellcheck of entire document has 
been completed†dialog box, and the last slide is selected. And click OK, the 
third slides is selected.
The second mistake is the logic of spellcheck is confusing.