Hi,
recently I upgraded Plasma on my Fedora 22 machine to 5.4.1 (from 5.3.2) and task manager started to show some general icon for some programs. For example instead of showing eclipse icon it shows this: http://i.imgur.com/cs1rwzv.png.

P.S.: I didn't file a bug yet, because I don't know whether it's bug on Plasma or on eclipse side.

Try changing the setting of "Use launcher icons for running applications" in the task manager settings.

Also see these bug reports:
https://bugs.kde.org/show_bug.cgi?id=352157
https://bugs.kde.org/show_bug.cgi?id=351624

It is supposedly fixed with this commit:
https://quickgit.kde.org/?p=plasma-work ... 44a905a677