"Compose" button disabled but no visible error if storage isn't enough

I had a test VIRSH pod deployed, with only 8Gb of disk (because it was itself a VM built with defaults).

When trying to compose a VM on it, by default the form is green and I can click "Compose", then I get an error on the disk size field, correctly saying that there's not enough space to make a 8Gb disk.

But, if instead of accepting a default I change some of the form default, for instance number of cores or memory, the "Compose" button gets disabled, and I don't see any indication of an error, unless I click on the storage "Location" dropdown for the disk, where I see the storage pool is grayed out and has an indication of not enough space.

I think in this case there should be an error visible directly on the form to why composing is not allowed.