about lower miou

[xc769458796]

I run evaluate.py with trained model from author(model.ckpt-30358) ,but miou is 0.3040,not is 0.7731,what is problem?thanks.
...
INFO:tensorflow:current step = 1400 (21.309 sec)
Intersection over Union for each class:
class 0: 0.8422
class 1: 0.3809
class 2: 0.1849
class 3: 0.3918
class 4: 0.3240
class 5: 0.3159
class 6: 0.2032
class 7: 0.3006
class 8: 0.3819
class 9: 0.2088
class 10: 0.2025
class 11: 0.1765
class 12: 0.3372
class 13: 0.2381
class 14: 0.2877
class 15: 0.3090
class 16: 0.1991
class 17: 0.2612
class 18: 0.2203
class 19: 0.2930
class 20: 0.3253
mean Intersection over Union: 0.3040
Pixel Accuracy: 0.8181

[Raulpathak]

I am also looking for an answer for this . Let see who can help us