Cannot indent a list item after undo step

Here are the steps to reproduce:

• type some text, like "foo bar"
• click the unordered list button from the tool bar
• place the caret at the beginning of the list item that has just been created, before the "f" in my case
• press Tab: the list item is indented correctly
• press Shift+Tab: the list item is outdented correctly
• now place the caret inside the list item, like after "foo"
• press Tab: 4 spaces are inserted correctly
• click the undo button from the tool bar
• place again the caret at the beginning of the list item, before the "f" in my case
• press Tab: this time, instead of indenting the list it inserts 4 spaces