You aren't putting any bounds on what it throws away when looking for your tag. Here is a more simple example. Here's the data:

a=1,b=2,a=2,a=3,b=4
[download]

If you search using /b(.+?)4/, you will match b=2,a=2,a=3,b=4 because the .+? expression doesn't care about what it discards to find your match.
In your code above, you match the first ELEMENT tag, but your .+? expressions only care about the part number; that is why they eat multiple ELEMENT tags on their way to it.
while you could do your match using very convoluted and fragile regexes, it is better to do it programatically. Since you only want to match within 1 record of your data, the first step should be splitting the input into records (demonstrated in another responce). then your regexes will be limited to just the 1 record you are searching