Node: Middle-clicks paste instead of toggling, Previous: x-symbol interoperation, Up: Known problems
This is probably the fault of your favorite package. In Emacs-21.1, the following culprits are known; Emacs-21.2 inherits those bugs, as of 21.3, they will be fixed. The patches have been thoroughly tested and applying them is hardly likely to cause any adverse effect.
Apply the patch in patches/flyspell.patch
.
Apply the patch in patches/mouse-drag.patch
.
This is one complicated mess to dig through. Better just end the search with <RET> before toggling and resume with C-s C-s or similar afterwards. Since previews over the current match will auto-open, anyway, this should not be much of a problem.