Hello Harald,
This mailing list is meant for discussions pertinent to TensorFlow development and the right channel for questions like yours is either GitHub issue (if you believe this is a bug) or StackOverflow (for general TensorFlow questions).
Having said that, the output shape of the batch dataset is determined at graph construction time and if at that point the drop remainder argument evaluates to true, then the first dimension output shape should indeed be equivalent to the batch size (implemented
here and tested
here). If however, the drop remainder argument is a tensor itself, then its value is not known at graph construction time and the first dimension of the output shape will be unknown.
If you would like to follow up, please create either a GitHub issue or StackOverflow question and reference it in your response.
Best,