[TYPO3-mvc] Migration of Extbase Extension from 4.4.4 to 4.5.4

[invigo]

Hi all,
we are currently stuggling at a little problem:

We are trying to migrate an Extbase-T3-Extension (Backend und 
Frontend-Plugin) from Typo3 4.4.4, Extbase 1.2.1, Fluid 1.2.1 to Typo3 
4.5.4 and we fail (and fail and fail) getting ajax working

The whole extension works under 4.5.4, but all ajax-calls just return 
blank pages (empty returns). It all looks like a forgotten template or 
that we did not introduce a method in etxt_localconf.php, but as already 
said, the extension works fine under 4.4.4 (tested in a blank new 
t3-installation) and fails in a new blank 4.5.4 installation, syslog 
remains empty as well.

Typoscript-Template-Snippet (Only Ajax-Part):

[typoscript]ajaxHtmlCallAjax = PAGE
ajaxHtmlCallAjax {
typeNum = 5000
config {
disableAllHeaderCode = 1
disablePrefixComment = 1

xhtml_cleaning = 0
no_cache = 1
admPanel = 0
}
}
extensionname_pi1 < ajaxHtmlCallAjax


extensionname_pi1 {

10 = USER
10 {
userFunc = tx_extbase_dispatcher->dispatch
pluginName = Pi1
extensionName = Extensionname

switchableControllerActions {
1 {
controller = FrontendCppMain
actions = 
screenselectprofile,screenselectobjective,screenselecttraining,screeneditidp
},
2 {
controller = FrontendAjax
actions = index
},
3 {
controller = FrontendIdpExplorer
actions = 
screenmyidps,screenmyidpshares,screensharedidps,screenregionalidps,screenmydialogues,screenregionaldialogues
},
4 {
controller = FrontendIdpManager
actions = 
screenidpnextsteps,screenidpoverview,screenjobprofiles,screenidpobjectives,screencareerdialogues,screenpersonalinfo,screenchangelog
}
5 {
controller = FrontendUserDetail
actions = 
screenlogindata,screenpersonaldata,screenmanagerdata,screenpassword,screenteam
}
6 {
controller = FrontendFileList
actions = screenregionalfiles
}
}
settings =< plugin.tx_extensionname.settings
persistence =< plugin.tx_extensionname.persistence
view =< plugin.tx_extensionname.view
}
}
[/typoscript]

Everything using pagetype 5000 returns nothing under 4.5.4.

We do not want to reengeneer the whole extention to fluid widgets (which 
would probably work), we just want our ajax back ;)


Any ideas? Thanks in advance for any hint!