Hi Henk,
That’s a strange one!
I would definitely go around the disti and contact Wyse support directly and see if they have come across this.
As a matter of interest what is the configuration of the device, any thing unusual? Do you have it pointing to a wlx.ini?
Finally if you are just using ICA or RDP you can convert them to a V10L however Wyse support would have to provide the files and its not an office supported process. I would be investigating why you have the image corruption first.
Cheers,
-TT