Ok. here is another test mediasink. closer to christoph's master, but without some changes that may cause extra audio issues.
I changed 3 setting that I could identify to tbe differnt. lets test if it made any difference - i may be broken even more.
there are other changes made by chrisophe relating to passing events to the basesink. those could also been broken somehow.
to get the the bottom of this you may have to start enigma2 from cmd line with some extra gstreamer debug set to caputre what is happening when you try Ffw /Rev or number jump.. but I need to work out appropriate cmd line first.

attached zip for testing as before.mediasink test2.zip

/Daz