So I've been having this problem consistently - it's not a huge deal, but I figured it's better to have a log of it than not? When attacking planet, one of my first two hits does not actually affect the population although the energy is used, the attack box pops up, and the red/blue spheres display.

If the planet window is kept open throughout attacking, the population bar will go down with the first hit, remain the same for the second hit, and then go down as normal for subsequent hits. If I close the planet window immediately after the first hit, the population will be full when I re-open the planet window and then will go down as normal with subsequent hits and opening/closing the planet window will not affect the population bar.

This only happens on planets where I'm consistently hitting for max damage - otherwise all of the damage logs just fine.

Edited to add: this is using the latest version of Opera on Windows 7.

Nothing wrong with your browser, long-running issue that can't be fixed if I recall correctly.
Hopefully Senator's advice from the thread linked below will sort you out.

viewtopic.php?p=432543#p432543