I keep getting the dialog "rdesktop is not responding" when running our rdesktop under gnome 3. I haven't completely pinpointed the conditions that trigger this, but it happens when doing Alt+Tab to switch back to the rdesktop window. Bug 5337 implemented _NET_WM_PING support, which might be when this issue started. This is with thinlinc-rdesktop-4.6.0post-5169.x86_64 and Fedora 23.
We'll start by diagnosing the issue.
I've seen this when running rdesktop in a ThinLinc session on SLES 12 as well.
The problem was also reported upstream issue [1], and a fix was commited [2]. [1] https://github.com/rdesktop/rdesktop/issues/76 [2] https://github.com/rdesktop/rdesktop/commit/14a4bf2d1dafb5a5db5b46a52e4435661d510953
I've used it a bit now, both directly on my workstation and in a ThinLinc session, and I cannot get this problem anymore. Should hopefully be solved now.