We have created a forgot password popup on the login page where we are generating Pega's captcha. The user has the ability to generate different captcha (by clicking on the captcha's refresh button). By doing so, the OOTB activity pyGenerateCaptcha is called and it generates a new captcha and stores it on the pxRequestor Page.
On submit on the forgot password popup, we need to validate that the user entered the correct captcha. For that, we need to retrieve the value of the captcha generated earlier by the activity pyGenerateCaptcha that is saved on the pxRequestor Page.
Our problem was that the pxRequestor still held the old value of the captcha and not the newly generated one.
I hope this explains our need to refresh the pxRequestor.