Maybe the IME is wrong. It depends on what kind of IME your using, for smartphone I'll recommend Simeji for you. It's so fun, easy and cute! It has varieties of keys also it has hiragana, katakana and when you hit space it will show you different kinds of kanji and so on.

no, it's correct... what do you mean saying "When I entered the romaji for a word (speak, for example), the right hiragana wasn't being shown."?... you typed "hanasu" and got "はなす", right?

I am going to say the same as Deepsoul, just make sure you selected the 「あ」chatacter from the drop down. Also, be careful when typing Japanese, because lower case letters are Hiragana, and upper case letters are Katakana. As for pressing spacebar, it shows all the possible kanji for kana, and you select one by using the up and down arrow keys, and then pressing space.

When you switch to the Japanese IME,beside the 【JP】there is an 【A】.You can click it to choose 【あ】（ひらがな）,then try to type.