Bumps on the Leaves of my Hibiscus

[Kelena]

This really is the least of my worries, I think, but I have several very tall hibiscus (red, non-native) that have little unattractive bumps all over them. They look like they have the mumps except the bumps are pretty close to the color of the leaves. The trees are flowering and seem otherwise healthy. I have a native white hibiscus growing between them and it doesn't seem to be bothered at all by bumps.

Seen this?