I downloaded and installed both Eclipse IDE and Nitrux icon theme, but I can't get Eclipse to update its panel icon correctly. Here is an image:
https://docs.google.com/file/d/0B2vSdKe1WI42YmdTeFI3ZFpqamM/edit
However, when Eclipse isn't running, the icon is fine (it replaces itself once Eclipse has been started). How can I fix this?

I'm afraid you'll need to adjust Eclipse itself to do this - KDE applications source their icons from the same place and so will often respect changes such as this one, but other applications do act differently unfortunately. The method you'll need to follow to adjust the icon tends to vary per application.

So how can I change the icon? I tried also to change in the desktop file of eclipse the Icon property, but nothing changed.
What's strange is that on my laptop there isn't such behaviour.

I've not seen the screenshot (just shows a "broken image" indicator here) but guess the taskbar will favor the icon that eclipse sets on the window.
If eclipse loads that icon from disk, you can search for ("strace eclipse 2>&1 | grep open") and replace it on disk.
Otherwise you'll likely have to file a bug against eclipse to use the (i guess) theme icon on the window.

Here's another link.
https://mega.co.nz/#!OJQHTayQ!Ug39iyycw ... wcx7p6zcCo
The output of strace is:

Code: Select all

open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
open("/lib/libpthread.so.0", O_RDONLY|O_CLOEXEC) = 3
open("/lib/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3
open("/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
open("/usr/share/eclipse/eclipse.ini", O_RDONLY) = 3
openat(AT_FDCWD, "/usr/share/eclipse//plugins/org.eclipse.equinox.launcher.gtk.linux.x86_64_1.1.200.v20130807-1835", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
open("/usr/share/eclipse//plugins/org.eclipse.equinox.launcher.gtk.linux.x86_64_1.1.200.v20130807-1835/eclipse_1506.so", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/share/eclipse//plugins", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/lib64/", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3

I don't see any icon loaded here...
Can I try something else or it's time to file a bug?

That seems to be the -fairly ugly- icon ecplise sets on the window (see the titlebar)
You can either request that the taskbar should prefer system icons under all circumstances (though the client may have good reason for altering the icon eg. to indicate a certain state) or eclipse to please load and use the theme icon in preference to the (hardcoded?) one for setting the window icon.
This *may* be an issue with the particular eclipse version (ie. depending on whether it's from your distro or a generic download)