I am not sure what the cause is for this. So in sentencepiece you typically have a special character ▁ before the subword token. In this case, apparently 13 in vocab is the empty token ▁. I am not sure why it is needed in this case though. For those who want to try stuff out, here is a MVCE:
from transformers import AlbertTokenizer

tokenizer = AlbertTokenizer.from_pretrained('albert-base-v2')
inputs = tokenizer.encode("The capital of France is [MASK].")
print(inputs)
# [2, 14, 1057, 16, 714, 25, 4, 13, 9, 3]
print(tokenizer.convert_ids_to_tokens(inputs))
# ['[CLS]', '▁the', '▁capital', '▁of', '▁france', '▁is', '[MASK]', '▁', '.', '[SEP]']
print(tokenizer.decode(inputs))
# [CLS] the capital of france is[MASK].[SEP]

Perhaps @lysandre (ALBERT)  or @mfuntowicz (tokenizers)  have an idea.