I cannot observe the problem, mouse releases map correctly and can be moved without moving the map - Mozilla/5.0 (Windows; U; Windows NT 5.1; de-DE; rv:1.8.1.6) Gecko/20070727 K-Meleon/1.1.2 (ax) - Logitech Optical Wheel Mouse, XPpro SP2, Pentium500 192MB RAM.
p. s. K-Meleon Mouse can be erratic at my PC when many things are loading at the same time - maybe check on that on Your PC.
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Bugs