The behavior is variable according to the calendar source:

Connection Between ListingsConnection to External Listings
The block will be removed as we were able to identify the source of the block and which event to delete from your calendar that is related to the removed block.The block must be manually removed, as events from external channels do not come with identifiers and as a result, we are unable to find the block related to the deleted activity on your external portal.

Now that you already know how behaves in relation to the exclusion of blocks in iCal connections, how about checking out more related topics on the subject?