Reauthentication Problem when using stufftodoplugin

[cforce]

I already files a bug at the stufftodo plugin (https://github.com/GOYELLO/goyello_stuff_to_do/issues/15) , but it looks more related to http-auth, however if i deinstall http-auth i don't get into this trouble.

The ajax request on "stuff_to_do" routes and/or time report api of redmine causes reauthentications in http-auth after the use already sucessfully made login.
Seems as the sessions cookie isn't used - maybe wrong realm..
We need http-auth only for webdav auth for redmine of plugin https://github.com/amartel/redmine_webdav.

Any ideas what the problem could be?
Would it be possible to enabled http-auth only for suburi /webdav and make standard form baed auth on website?