I think what you are seeing has to do with the two type of text layers that Photoshop supports. There is the Plain Text layer and there is a paragraph text layer. Both can contain lines of text. A plain text layer can be transformed more freely then a paragraph and line will not change it like transforming a raster layer in size. Paragraph Text layers the text is flow or wrapped into the paragraph area. When to transform are paragraph text layer you changing the size of the area text is flowed into. Here are two text layers in two screen captures. I changed the text point size in the two captures the area size does not change just the text size read the text in the two screen captures the text was not changed.