@aignashev. Thanks for asking. To be honest, I don’t know. This is just something that happens as a result of how Mootools does transitions. it is actually an issue with Mootools’ reveal/dissolve Fx functions. I had a similar problem with jQuery. The only difference with jQuery is that the problem was seen in different browsers.
This is why I list it as a known issue. It is something that I have little to no control over. Someone could argue that I could customize the Mootools code to get it to work. However, that may have undesirable side effects or conflicts to other code that uses the reveal/dissolve Fx functions. I prefer to stick with the standard code.