I didn't know about CCM_SETUNICODEFORMAT and WM_NOTIFYFORMAT, thanks for information (btw. MSDN says from IE5.0). But, could it be possible that KernelEx automatically uses one of those two methods for unicode apps? For example, app is unicode (made for NT family of windows) and uses unicode data in WM_NOTIFY, but author didn't know about existence of KernelEx and possibility that his app will be used on Win98 so he didn't implement CCM_SETUNICODEFORMAT or WM_NOTIFYFORMAT.
Would you consider implementing support for unicode notifications LVN_GETDISPINFOW (for listviews) and TTN_GETDISPINFOW (for tooltips)? LVN_GETDISPINFO is sent by a list-view control to its parent window, message is sent when list-view control has style LVS_OWNERDATA. Unicode app expects notification LVN_GETDISPINFOW but list-view control sends LVN_GETDISPINFOA, so list-view ends up without any strings. TTN_GETDISPINFO is not that important, but those two messages are very similar so if you manage to implement one it should not be too hard to implement other one as well.