I came to know that people fast on the day of Mairaj. I looked up in Hadith books but no mention of it. Scholars here in Saudi Arabia believe it is Bid`ah as there are no authentic Hadith proving its validity.
The reverence which the Muslims, mostly of the sub-continent, give to the night of 15th Sha`baan is not supported by any dependable narrative ascribed to the Prophet (pbuh). Therefore, I do not think that this night should be held in any kind of veneration. I agree with the scholars that you have referred to in this case. But this does not mean that it is prohibited to fast on this day. All that it means is that it is wrong to hold this night, in any way, above any other night of the year.