ibdata1 grows when .idb files are moved to another disk

We have an installation with data directory residing on a disk which is close to being full.

To make space available, we have moved some huge .ibd files to another disk, with a symlink from the the data directory.

While this does free up disk space immediately, we have observed that over the course days, the ibdata1 file grows proportionally to the size of the .idb files that were moved, effectively cancelling out the attempt to free up disk space.

We're wondering if this is expected behavior.