Updated Aug 16th: Jump Desktop 4.0.5 has been released on the App Store - it contains the fix to this issue. Be sure to upgrade if you're hitting this issue.

Snow Leopard 10.6.8 has a bug in it's VNC Server which prevents right mouse clicks from being sent properly to the machine. A work around for this problem exists: Press the Ctrl key in Jump and then do a left click instead - this is equivalent to a right click.

This issue only effects Snow Leopard version 10.6.8.  

We're investigating an automated work around for this.

Update Aug 8th: Jump Desktop 4.0.5 has been submitted to Apple which contains the fix.