In MSCA, the rules surrounding the ownership of project results are the same as those applicable in other Horizon 2020 actions: project results are owned by the beneficiary generating them.
This means that even the results generated by your fellow while on secondment would belong to your institution, in accordance with the default rules applicable in the Grant Agreement. In other words, your partner organisation will not automatically be entitled to any IPR over the results developed on secondment, since it is not a beneficiary in the project, but a mere third party which does not employ the researcher within the action but only provides additional training and hosts him during the secondment.
However, this default rule is not always compatible with a third party institution’s internal policy. It is indeed not uncommon for partner organisations to require that the ownership of the results developed on secondment be granted to them, because this is what their IP policy requires. For this reason, and to avoid any dead-end, your institution should adopt a flexible approach. Since your partner organisation might not be aware of your own obligations under the Grant Agreement, you should clarify this point beforehand and outline your rights and obligations in terms of ownership, access rights, protection, exploitation and dissemination. This will allow your partner to understand the framework in which you can negotiate, and the rules and limitations which you have to comply with on your side. Then, remember that the Grant Agreement allows you to license or to transfer project results to third parties, under certain conditions. This means that, providing that these conditions are met, you can agree to license or transfer to your partner institution the project results developed by your fellow while on secondment. The terms of such agreement will vary depending on both parties’ interests, but this will allow you to settle on a different ownership regime which will be beneficial to you and your partner alike.