model_main.py does not save max checkpoints as specified

System information

• What is the top-level directory of the model you are using:
  https://github.com/tensorflow/models/blob/master/research/object_detection/

• Have I written custom code (as opposed to using a stock example script provided in TensorFlow):
  No

• OS Platform and Distribution (e.g., Linux Ubuntu 16.04):
  Linux ubuntu 16.04

• TensorFlow installed from (source or binary):
  anaconda

• TensorFlow version (use command below):
  1.13

• Bazel version (if compiling from source):

• CUDA/cuDNN version:
  CUDA 10.0.130

• GPU model and memory:
  GTX 2080Ti 11 Gb

• Exact command to reproduce:

python /home/admin/code/models/research/object_detection/model_main.py \
    --pipeline_config_path=${PIPELINE_CONFIG_PATH} \
    --model_dir=${MODEL_DIR} \
    --alsologtostderr

Describe the problem

I use the config as config = tf.estimator.RunConfig(model_dir=FLAGS.model_dir, save_checkpoints_secs=900, keep_checkpoint_max=100) in model_main.py, the save_checkpoints_secs is effective, it save checkpoint every 15 minutes, but keep_checkpoint_max is not effective, there are only 5 models at most