Magento randomly redirects to hostname/index.php/install/

We had this problem and now have both a cause and a solution.

The error behavior (redirecting to the Magento install wizard after a sucessful upgrade) is not random. It occurs when the SOAP API URL is hit. In our case we had a scheduled process that hit the SOAP API periodically. so it would occur, then go away then reoccur.

After time the behavior goes away. To make it happen... Load yourAPI URL in a browser http://hostname.com/api/soap/?wsdl The magento admin and likely the front end store pages will throw the 404/install.php page.

The cause of the issue was a PHP bug https://bugs.php.net/bug.php?id=62577 and Magento was able to provide a patch PATCH_SUPEE-3762_EE_1.14.0.1_v1.sh We were running Redhat 6 with PHP 5.3.3 (but this still occurs in PHP 5.3.28)

Alright this is the solution that fixed the problem I was having.

Step 1: Clear /var/cache and /var/session

Step 2: Reboot server

Step 3: Wonder why that just worked......

I plan on doing some more research on this problem.

Thanks to all that took the time to read and help.

Update

Here is the error that triggers the event.

[Thu Jul 24 08:20:40 2014] [error] [client 10.0.0.115] PHP Fatal error: SOAP-ERROR: Parsing WSDL: Couldn't load from 'http://host.com/index.php/api/soap/index/?wsdl=1&wsdl%2F_vti_bin%2FListData_svc%2F%24metadata=' : failed to load external entity "http:// host.com/index.php/api/soap/index/?wsdl=1&wsdl%2F_vti_bin%2FListData_svc%2F%24metadata="\n in /var/www/html/lib/Zend/Soap/Server.php on line 811

[Thu Jul 24 08:20:46 2014] [error] [client 10.0.0.115] PHP Fatal error: SOAP-ERROR: Parsing WSDL: Couldn't find in 'http:// host/index.php/api/soap/index/?wsdl=1&wsdl%2Fmex=' in /var/www/html/lib/Zend/Soap/Server.php on line 811

Edit: 07-25-14

I got this error when adding a reference to a solution in visual studio.

I discovered that visual studio 2012 does not play well with soap v1. These following links ruin my site in visual studio, but work just fine in SOAPUI.

http://magentohost/api/?wsdl
http://magentohost/api/soap/?wsdl