Why does Minecraft Classic show the menu when mining/placing blocks?

When I play Minecraft Classic, sometimes the menu screen appears when mining/hitting/placing blocks. It starts to get annoying when you are trying to make a giant house. So my question is why does it appear, and how to remove/prevent it.


Solution 1:

Bit of a late answer, but it's because the client is somehow losing focus when clicking. This is mostly because of Java changing something in mouse handling, and the older LWJGL not expecting a change.

You can downgrade to java6 to play it without this issue.