Redirect to 'referrer' does not work when short="true" or "false" (Works when set to "emailonly")

[MaryOJob]

Describe the bug
When redirect to referrer is set in the signup shortcode (on a content that is not restricted to any membership level) and "short" is set to either "true" or "false", the redirect to referrer does not work after the member checks out, they are taken to the membership confirmation page instead of the last piece of content they were viewing.

To Reproduce
Steps to reproduce the behavior:

1. Activate Signup Shortcode Add On
2. Go to any piece of free content (page or post), add this shortcode:
   [pmpro_signup submit_button="Unlock Your Account Now!" short="false" level="2" login="2" redirect="referrer"] or [pmpro_signup submit_button="Unlock Your Account Now!" short="true" level="2" login="2" redirect="referrer"]
3. Go to a new browser and sign up on the content you have added this signup shortcode to with the above parameters, where 2 should be replaced with the level ID of your paid membership level.
4. Check out, you would not be redirected to the piece of content you just viewed.
5. However, if you set your shortcode to [pmpro_signup submit_button="Unlock Your Account Now!" short="emailonly" level="2" login="2" redirect="referrer"], you will be redirected to the last piece of content viewed after checking out.

Screenshots

Expected behavior
When the attribute short is set to true, false, and emailonly on a piece of content (page or post) where the level ID is set to that of a paid membership, the member should be redirected to the last piece of content they viewed before checking out.

Isolating the problem (mark completed items with an [x]):

• I have deactivated other plugins and confirmed this bug occurs when only Paid Memberships Pro plugin is active.
• This bug happens with a default WordPress theme active, or Memberlite.
• I can reproduce this bug consistently using the steps above.

WordPress Environment

- PMPro V. 2.5.5 - WordPress 5.6.2 - PHP version 7.4.14 - Paid Memberships Pro - Signup Shortcode Add On | Version 0.3

[jeeemmyy]

Mine is not working even when used short="emailonly"

[JarrydLong]

I've tested this with Paid Memberships Pro 2.9.8 and Signup Shortcode Add On 0.3 with both emailonly and all fields present, and the referrer appears to work as expected in the current versions.

[dvozov]

Referrer stopped working for us, too, when we switched to Stripe Checkout a couple of weeks ago. Before that, it was working fine.

By "working fine", I mean that new free signups were sent to the Membership Homepage designated in their level.

By "stopped working", I mean that once we went to Stripe Checkout, after someone signed up for a free account, the free membership was created but the signup page simply reloaded. So, the customer saw no feedback that their account had been made. I thought that this behavior was just on our site, using the combo of addons we have. We created a workaround because we're very motivated to use Stripe Checkout.

Reading comments here, I just now tried disabling the signup shortcode addon on our staging site, and now the referrer is "broken" in a different way. Instead of directing to where it should (a page with their free content), they're directed to the default confirmation page for their level. I'm assuming that we see this behavior due to using the beta Stripe Checkout system active on the site. The confirmation page isn't a deal breaker, but from my POV, it's better to just send new free members to their free stuff.

I hope that this feedback is helpful. When updates are made to any addons we use, we always try them. Seldom are there issues. In fact, I think that this is the only set of gotcha's we've encountered. Thanks for your hard work :)