`mv` adds additional subfolder when subfolder exists

[boraberke]

When mv is used to move a file between buckets, it behaves differently depending on whether a subfolder with the same name exists.

Reproducing steps

1. Create two buckets, test-bucket and test-bucket-2.
2. Create a temp file in your local dir.

   touch 12345.txt

3. Copy the file to test-bucket with the following subfolders.

   gsutil cp 12345.txt gs://test-bucket/folder/nested_folder/aaaa/bbbb/cccc/12345.txt 

4. Move file to test-bucket-2.

   gsutil -m mv gs://test-bucket/folder/nested_folder gs://test-bucket-2/folder/nested_folder

5. Check the contents of test-bucket-2.

   gsutil ls "gs://test-bucket-2/folder/nested_folder/**"

   First Output should be as follows:

   gs://test-bucket-2/folder/nested_folder/aaaa/bbbb/cccc/12345.txt

6. Repeat the step 3, 4 and 5. Check that output of step 5 included a secondary nested_folder in it.

   gs://test-bucket-2/folder/nested_folder/aaaa/bbbb/cccc/12345.txt
   gs://test-bucket-2/folder/nested_folder/nested_folder/aaaa/bbbb/cccc/12345.txt

I am not sure if this is an expected behavior but same command producing two different results depending on the bucket structure does not feel right.