hm, does hkn say anything else, when you use oem3 + a mouse button?
(like executing clickmouse.... (in blue color))

Another point might be, that your settings for mousedelay are to low and you have to rise them, this can be done in the options dialog of hotkeynet.
For more detail how to do this see: http://hotkeynet.com/ref/clickmouse.html