Why can not I format a text in gmail on a Kitkat android tablet?

[AC Question]

While composing an Email using gmail, the text could not get formatted, you still can select and hold a specific word or sentence and press the "Format" option, and nothing happens, no format panel appears and the format option disappears for good.

"I am using Samsung tablet E, android kitkat 4.4.4".

Any ideas? ... thanks.