I do see another possible problem though. The trigger will run each time a unit enters the region. Say you have 5 marines running to the region. The trigger will run 5 times. The first 3 will be skipped since there are only 1, 2, 3 units in the region. However, marine 4 and 5 will both trigger the... uuh, trigger. Since you are waiting 1 second before you remove any units, the trigger will successfully run twice, and give you 3+3 battlecruisers even though you only had 5 marines. Remove the wait 1 second.
Ah, I think i figured out how your Unit - Remove looks. Your problem is that you are removing unit number 4 from the unit group. the number after unit in unit group is the index that identifies each unit. So you are just removing a single unit that happens to have index 4.