From my early tests with iOS 9 GM Seed it looks like Apple has made some “annoying” changes to the way inter-app communications is handled.
When one 3rd party app attempts to call another 3rd party app the user is prompted with a message ‘“App1” wants to open “App2”’ and the user is given an option to Open or Cancel.
Now this seems to happen only once but for every combination.
Example in XenMobile terms:
If you click on web a link in WorxMail you will get a prompt ‘"WorxMail wants to open “WorxWeb”’. Upon using the new iOS function “Back to WorxMail” you will get another prompt ‘“WorxWeb” wants to open “WorxMail”’
There does not seem to be a work around and users just have to go through all combinations before these messages dissapear.