blockchain.get_ordered_blocks() does not iterate all blocks

When I iterate the blockchain the loop over the blocks above finishes at block 478560/774513. I have no clue why
```python
for block in blockchain.get_ordered_blocks(index=index, cache=cache_file):
    print("\rblk %d/%d" % (block.height, len(blockchain.blockIndexes)), end='')
print("\nBye")
```

ends with exit_success (0)
```
0 ms blk 478560/774513
Bye
```