Regular Expression Range not working as intended for verifying randomly generated passwords

I am trying to verify passwords generated using a random password generator function by using regular expression in C++.

the rules for the passwords are: The password has to be 8 letters total length. the password can be 4 capital alphabets and 4 numbers or 6 capital alphabets and 2 numbers.

Valid Examples:

• ABCD1234
• PQRSTU88

I am using this expression: /^(?=.{8}$)([A-Z]{4,6})([0-9]{2,4})\w+/gm

and this website to test the expression: http://regexr.com/3frd4

it works when the range is kept as {1,4} but if I change the range to {2,4} the second example password fails.

Clicking on the details button shows that for the first example password: ABCD1234,

Capturing Group #1 captures ABCD & Capturing Group #2 captures only 123 (not 1234?).

For the second example password: PQRSTU88,

Capturing Group #1 captures PQRSTU & Capturing Group #2 captures only 8 (not 88?).

from what I understand {2,4} specifies at least 2 numbers to at most 4 numbers. Then why is my regex not working for that range in case of the second example.