Based on this link it is safe to assume that, rather than relying on ubuntu for the installation, you should shrink/resize your partitions (manually) than allowing ubuntu to handle the partitions for you.
Understand that the risks involved in relying on ubuntu for creating partition for you.
If I were in your place I would never go for install alongside windows option, and create and choose the partition by myself.
BTW I had used that option of installing alongside windows, but I had already shrinked my partitions in windows, ubuntu was installed in the free space created by shrinking the partitions.