An old bug, that I have been trying to avoid for at least two years. Briefly, from bug 272042 comment 7: 

> … recurred today after I allowed net/citrix_ica … to make the local 
> desktop environment – with /usr/local/bin/wfica as a part – 
> completely unusable. 
> 
> After inadvertently bringing to the foreground something other than wfica: 
> it's impossible to switch between applications, and so the wfica view of 
> the remote desktop can not be used to apply the long-winded and fragile 
> workaround that's normally necessary to avoid this blockage. …

There are multiple aspects to the workaround. Behaviours, during the minutes before the workaround becomes effective, are not entirely predictable. Sometimes it's as if there's an element of luck. 

Steps to workaround, condensed: 

 1. ignore bug 258117 (unwanted full screen, maybe spanning 
    multiple displays)

 2. ignore general flickering

 3. take great care to not inadvertently switch away from the wfica window 
    (do not Alt-Tab, and so on)

 4. point at an edge of the remote screen where, otherwise, the local 
    desktop environment would change appearance in response to pointing 
    – I usually aim for the left, where I have (in Plasma) a panel that 
    includes Task Manager

 5. observe rapid localised flickering and do not shy away from this, it 
    seems to be an essential step towards avoiding blockage

 6. when remote (e.g. Windows) desktop icons appear, double-click on an app 
    that may be likely to accelerate the workaround (I typically aim first 
    for Remote Desktop i.e. mstsc)

 7. observe nothing, as if the app has not been opened

 8. again, move the pointer to an edge of the remote screen that will cause 
    rapid localised flickering

 9. observe opening of the app that was opened at step (6)

10. after the app window is in front, move the pointer away from the 
    rapidly flickering area, to an area of the top of the screen where the 
    Citrix palette should appear

11. do not be disconcerted by rapid flickering that might also occur in this
    area

12. click

13. rinse and repeat some steps above until, finally, a click somewhere at 
    the top of the remote screen triggers visibility of the Citrix palette

14. if all palette fonts are illegible (a bug that is not yet reported), 
    then click the icon that looks most like a window

15. take great care to click nothing other than the wfica window

16. if window controls within the title bar are out of sight, carefully 
    drag the title bar until controls become visible, then use a control to 
    make the window a size that will be usable

17. observe that the local desktop environment froze when wfica began its 
    remote desktop connection

18. resist temptation – take great care to click nothing within the local 
    desktop environment; refrain from Alt-Tab; and so on

19. be patient

20. await an indication that the freeze of the local desktop environment has 
    ended. 


I have a clock, showing seconds, at the foot of the panel to the left of the left-most screen.