Steps to reproduce:

• Create a 3D project
• Import some image asset to project
• Open Texture Editor
• Create a new texture
• Set Texture -> Source to the imported image
• -> preview images in Texture Editor and Material Browser update correctly
• Click action icon beside Texture -> Source and choose "Reset"
• -> Source seems to be removed but image preview for texture still shows the imported image
• Add new texture in Material Browser -> Textures -> +
• -> preview image for the first texture updates now in Material Browser, but Texture Editor still shows the old image and Source value is again the imported image.