Thanks jimking. It would be great, if Tony could have look on it.
Here is another very good example from the Nirsoft's Utilies (
http://www.nirsoft.net)
*:
In this program the tooltips do
not work:
ActiveX Compatibility Manager v1.00 (
http://www.nirsoft.net/utils/acm.html) [file size: 36 kb]
while in this program they are
working properly:
ActiveXHelper v1.12 (
http://www.nirsoft.net/utils/axhelper.html) [file size: 40 kb]
I was comparing the names of their loaded DLLs and could not see any differences

(and both are 32-bit applications).
Anyway, maybe it's a good start to find out what causes the issue and if it can be reproduced/confirmed on other systems too.
(I have two different systems here with the same XWidget issue: Windows 8.1 Pro 64-bit / Windows 7 Home Premium 64-bit)
----
* they do not require any installation and do not write anything to the registry.