I came accross this bug as well. I fixed it with some custom CSS (at least for up to 4 columns):
.gallery .gallery-item {
float: left;
margin-top: 10px;
text-align: center;
}
.gallery-columns-1 .gallery-item {
width: 100%;
}
.gallery-columns-2 .gallery-item {
width: 50%;
}
.gallery-columns-3 .gallery-item {
width: 33%;
}
.gallery-columns-4 .gallery-item {
width: 25%;
}