It has nothing to do with your IDs. Tooltips don't send the ANSI notification, that's all.
Try something along these lines... and yes, I know it's assembler and this is a C forum.
.if uMsg==WM_NOTIFY
.if [ecx.NMHDR.code]==TTN_GETDISPINFOW
lea edi, lvh
invoke GetCursorPos, edi
invoke ScreenToClient, hList, edi
movi [edi.LV_HITTESTINFO.flags], LVHT_ONITEM
invoke SendMessage, hList, LVM_HITTEST, 0, edi