I have found since iOS8 that if the application is run in full screen it seems to lose the session when it loses focus.
Possibly web-app behavior has been improved in newer versions of iOS8.
Are you using the latest version of iOS8 to test this?
Is this really TMS iPhone controls specific?
Did you try this with regular IntraWeb controls and if the problem is there too, this rather looks like an iOS8 and/or IntraWeb issue. Our components itself do just use the IntraWeb session management like any other IntraWeb control but do not interfere/change/affect its operation.