'Random' Questions not all that random

For my project there are 5 question banks, each relating to a specific category. After the user correctly answers a question from bank 1, they advance to bank 2. If they do not answer correctly, they are given a new question from the same bank. Each bank has 5 questions in it. I would expect, even with randomizing the draw, you could expect to get the same question after an incorrect answer on occasion. Without exception, once you answer the question incorrectly, you receive the same question again (with your previous answer still in the box in the case of text/numeric entry) and again and again. I've attached the question loop, and if you can offer any insight, I would really appreciate it. Thank you!