I have 3 formula fields. The formula is basically this:

I had one field like that in my application for months. In report it is shown as number.

Today I wanted to add now formula field:

(((Date3 - Date2)  /  86400000)).toLong()

That shows up now in the report as text (the values are calculated correctly)

What is misterious is that if I make another formula field (3rd) and copy the formula from the first one

(((Date1 - Date2)  /  86400000)).toLong()

That too now is shown as text format, not number.

What is going on here?