ximbietc It's not a bug.
All package managers work the same in that regard.
If you install a new package, and it depends on another package that had received an update that you have not installed, installing it will result in a partial upgrade which might result in breakage.
Same thing happens If a dependency of a package depends on a package that had been updated.
Partial updates / upgrades are a no-go on any rolling distribution.
As to eopkg, I don't have proper expertise to judge what would be the best behaviour.
Anyways, a new package manager is planned for Solus, so there's really no point in trying to make any changes to eopkg.
It'll be replaced in the future, and any additional changes to eopkg would just go to waste, they'd be a waste of time, that could be better spent working towards other improvements to Solus.