Issue while updating the data in Datasource

I am currently using the druid-Incubating-0.16.0 version. As mentioned in https://druid.apache.org/docs/latest/tutorials/tutorial-update-data.html tutorial link, we can use combining firehose to update and merge the data for a data source.

Step : 1
I am using the same sample data with initial structure as

┌──────────────────────────┬──────────┬───────┬────────┐
│ __time                   │ animal   │ count │ number │
├──────────────────────────┼──────────┼───────┼────────┤
│ 2018-01-01T01:01:00.000Z │ tiger    │     1 │    100 │
│ 2018-01-01T03:01:00.000Z │ aardvark │     1 │     42 │
│ 2018-01-01T03:01:00.000Z │ giraffe  │     1 │  14124 │
└──────────────────────────┴──────────┴───────┴────────┘

Step 2:
I updated the data for tiger with {“timestamp”:“2018-01-01T01:01:35Z”,“animal”:“tiger”, “number”:30} with appendToExisting = false and rollUp = true and found the result

┌──────────────────────────┬──────────┬───────┬────────┐
│ __time                   │ animal   │ count │ number │
├──────────────────────────┼──────────┼───────┼────────┤
│ 2018-01-01T01:01:00.000Z │ tiger    │     2 │    130 │
│ 2018-01-01T03:01:00.000Z │ aardvark │     1 │     42 │
│ 2018-01-01T03:01:00.000Z │ giraffe  │     1 │  14124 │
└──────────────────────────┴──────────┴───────┴────────┘

Step 3:
Now i am updating giraffe with {“timestamp”:“2018-01-01T03:01:35Z”,“animal”:“giraffe”, “number”:30} with appendToExisting = false and rollUp = true and getting the following result

┌──────────────────────────┬──────────┬───────┬────────┐
│ __time                   │ animal   │ count │ number │
├──────────────────────────┼──────────┼───────┼────────┤
│ 2018-01-01T01:01:00.000Z │ tiger    │     1 │    130 │
│ 2018-01-01T03:01:00.000Z │ aardvark │     1 │     42 │
│ 2018-01-01T03:01:00.000Z │ giraffe  │     2 │  14154 │
└──────────────────────────┴──────────┴───────┴────────┘

My doubt is, In step 3 the count of the tiger is getting decreased by 1 but I think it should not be changed since there are no changes in step 3 for tiger and there is no number change also

FYI, count and number are metricSpec and they are count and longSum respectively.
Please clarify.