Ubiquity format partition on filesystem change even "format" is not set. Potential data loss.

For some reason, Ubiquity recognized my ext4 partition as ext2. So I set up the proper filesystem type - ext4, proper mount point, and didn't (checked it twice) set a checkbox "format partition".

After installation the partition was formatted.

Steps to reproduce:

0. Set up a virtual machine, to avoid actual data loss.
1. Create a test partition with an ext2 filesystem.
2. Store some test data on it.
3. Run Ubiquity installer and create some other partitions needed to install Ubuntu.
4. Set a mountpoint for the test partition, change a filesystem type, do not set "format partition" checkbox.
5. Install Ubuntu.

Expected result:
Test data will be stored on a test partittion, Ubuntu will fail to boot due to filesystem mismatch.

Actual result:
Test partititon will be empty.

This issue can be resolved in two ways:
1. If formatting partition should be be mandatory, the checkbox "format partition" must be set up and disabled, so the user will know, that the partition will be formatted.
2. If formatting partition is not mandatory, then Ubiquity shouldn't format the partition.