Hi Denis,
In the section for putaway in settings for warehouse storage type, there is a flag for 'Mix Stock Types'. The default value is blank which indicates that stock types are mixed in HU/bin . However, if you set it to 'X', then system will not allow mixing of multiple stock types in a HU in the storage type.
Whether or not system should allow HUs with different stock types in the bin will depend on the level of available qty indicator. If level of available qty is set to bin level, system will allow only HUs with same stock types in the storage type.
Regards,
Namita