setData triggers additional glTextureSubImage call for 1D array texture layer 0

When calling setData on a layered texture (I did not test others) there is an additonal call to glTextureSubImage that is unexpected (for me).

When tracing the attached program with apitrace, the setData line creates the following trace entries:

glTextureSubImage2DEXT(texture = 1, target = GL_TEXTURE_1D_ARRAY, level = 0, xoffset = 0, yoffset = 1, width = 100, height = 1, format = GL_RGBA, type = GL_FLOAT, pixels = [binary data, size = 1.5625 kb])
glTextureSubImage2DEXT(texture = 1, target = GL_TEXTURE_1D_ARRAY, level = 0, xoffset = 0, yoffset = 0, width = 100, height = 1, format = GL_RGBA, type = GL_FLOAT, pixels = [binary data, size = 1.5625 kb])

The first call to TextureSubImage does what I expected from the setData call and the second one sets exactly the same data but on level zero which I didn't expect.

I noticed this in an application where the level zero contained invalid data: the data from the last level. Each setData call triggered two glTextureSubImage calls of which the latter was always assigning the data to level 0.

At first I thought I could work around this by using the setData overload without a layer to upload all layers at once but this overload also just works on layer 0. This is somewhat confusing and should probably be noted in the documentation. (I guessed from the apitrace and confirmed it by perusing the Qt sources.)

This leaves me the following workarounds:

• not using the setData members for data upload on (1D)Array textures
• calling setData for layer 0 after all other layers

Maybe I made a mistake when setting up the texture (I find the documentation about this lacking). However, I believe the unconditional upload to layer 0 indicates an error.