Do any finance tutors out there know why this is?

Please and thank you!

Explain why the optimal weights on the risky assets change so drastically when going from the optimal 7%-mean, short-selling-allowed portfolio using the 4 risky assets to the optimal 7%-mean, short-selling-allowed portfolio using the 5 assets (4 risky + 1 riskless). Be as clear as you can. Explain why the optimal weights on the risky assets change so drastically when going from the optimal 7%-mean, short-selling-allowed portfolio using the 4 risky assets to the optimal 7%-mean, short-selling-allowed portfolio using the 5 assets (4 risky + 1 riskless). Be as clear as you can