Steps to reproduce the issue

Fresh install of joomla 3.7.3

1. Add a new Contact
   a. linked to Super user
2. Add a new Menu item of type „Single contact“ and select added contact from step 1
3. Extensions – Plugins
   a. Enable „Captcha – ReCaptcha“ Plugin
   b. Go to Plugin configuration and enter dummy string into „Site key“ and „Secret Key“ (for ex. „xxx“)
4. Global Configuration – Site – Default Captcha: Set to „ReCaptcha“
5. Go to front-end and select menu created in step 2)
   Then select „Contact form“ and enter something into “Name”, “Email”, “Subject” and “Message” field. Then press “Send Email”

Expected result

Postback, then message box that captcha wasn't set and still filled Textboxes

Actual result

Postback with messagebox, but all textboxes are empty so user has to enter again everything

System information (as much as possible)

Problem didn't occur before 3.7.3
PHP 5.4.16
Win7 Business Edition SP1
Apache 2.4.4.
Mysql 5.0.10

Additional comments

Hint to solution/reason:

I don’t know what’s the line for but in file “components\com_contact\views\contact\view.html.php” line 75 the contact data will be overwritten with category id. If this line is commented out it works. You can enter something in contact form, if you don’t enter captcha data and submit no data will be lost in textboxes and user don’t need to enter again.

$app->setUserState('com_contact.contact.data', array('catid' => $item->catid));