Infopath is a funny beast …
The upload a new form template from Central Admin was stuck and then unlock itself and stuck again a few days later….
We now found out the main issue : a disc space issue on the web front end server.
And caused by.. infopath solutions, as all the previous Solutions that were uploaded / deployed on the server do not get deleted and therefore polluted the directory C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\TEMPLATE\FEATURES, with a few Gigs of unused solutions.
So check that folder next time as SharePoint is silly sometimes !