...is in "edit view" (I mean, while I've the GUI Instrument, i.e. Kontakt 4, open to load patches)... 
It doesn't in "mixer view"!
I'll try to clear it...:
I've got my VEPro Instance on a second display... Logic on my main one.
I open, into the Instance, in a channel strip, a Kontakt 4 to load my patches... as soon as I click on the Logic's Arrange page, leaving the GUI of Kontakt open, the Instance disappear!
To see it again, I've to open the VEPro Server Interface plugin and click on the VE button... or bringing up the VEPro Server from the desktop... but it's useless... 'cause as I click again into Logic... PUF! ...disappeared again!
If I close the Kontakt's GUI, going back to the "mixer view" in the Instance, there's not problem at all! 
I've tried delete Preferences, reinstall the VEPro... no change. It happens in Logic 32 or 64 bit-mode. The last installation on my system was Kontakt 4... could be, strange enough, his fault? (before using K 3.5 I've not the same problem... but if I use K 3.5 into the instance now, and NOT K4, the problem is still there...)
My setup: MacOS X.6.3 - Logic 9.1.1 - Kontakt 4.0.5 - VEPro 4.0.5436
In the meantime, while waiting for someone suggestion here, I'll try to go back one version of VEpro...
Cheers!