This is sourcelink solution 11249750 - if you can access sourcelink.cadence.com take a look there.Originally posted in cdnusers.org by adbeckett
Essentially it's a bug, and you need to also define the bindkey for Ctrl Btn2Down - can be a dummy SKILL expression that gets evaluated (e.g. "t").
The same thing happens with shift modifiers, and in fact happens for all mouse drawthrus (1,2,3) - but you don't normally notice it for the other two, because they usually have the BtnXDown bindkeys defined.
It's fixed in IC610 - there will not be a need to define the Btn2Down binding with the same modifier then.