You highlight a bomb powerup and it changes your pointer to 3x3 size showing you the area you can bomb. Don't detonate it, instead click on the rocket and it should turn into horizontal line, but instead it changes to 1x1 size that does nothing. Clicking back on bomb won't change the the pointer to 3x3 either. To reset this behavior I clicked on different power-up (it asks if you want to buy it and I selected 'no'). It's a small thing, barely even noticeable.