2 Nissan (Vayikra)

The Ba'al Haturim on Vayikra 1,1 says that the reason the aleph of Vayikra is written small is because Moshe wanted it to say Vayikar (without the aleph) implying that it was more of a chance, (like what it says by Bilam), because of his humility. Hashem wanted it to say Vayikra, to show Hashem went out of his way to come to Moshe out of his great love of him,so they wrote the aleph small. Why is this the only time Moshe has a problem? It says Vayikra in Shemos 3:4 (Vayikra Eilov) and Shemos 19:20 (Vayikra Hashem Limoshe) and its written normally with a regular aleph, why?