I ran into this issue when I upgraded from Phaser 2.4.3 to 2.4.4. I use null sprites quite a bit to define hit areas over text, and in Phaser 2.4.4 I noticed that Phaser was using whatever the last created texture and displaying it on the null sprite instead of no texture.

Here's a test case with both a text sprite and some bitmap data:

https://jsfiddle.net/tanptet2/5/

Once the jsFiddle loads, you may have to hit "run" to see the duplicated textures.

In Phaser 2.4.3 and below, the null sprite would not have a visible texture of any kind.