Grub2 with triple boot W7+W10+(k)Ubuntu

A while ago I installed Kubuntu next to W7 on my laptop and Grub2 detected W7 without any issues.
Recently I added W10 to the dual boot and that's where it gets a little weird.

First of, the not weird part: the W10 installer got rid of Grub2, I was expecting that. I solved this by booting into a Kubuntu live environment, mounting the Kubuntu partition and then reinstall Grub2, followed by ruing update-grub.

After ruing update-grub I was expecting both W7 and W10 to appear in Grub2, but that wasn't the case. Instead of Kubuntu and an entry for W7 (like it was before), it now contains an entry for Kubuntu and one for W10, not W7.

After selecting W10 and waiting for a short time (the W10 OS-selection menu takes some time to load apparently), I get the W10 OS-selection menu that displays W10 and W7. Selecting W10 boots directly to W10, but selecting W7 causes a reset of my laptop after which I have to select W10 in Grub2 again and then it immediately starts W7, skipping the W10 OS-selection menu.
After I shutdown or reboot W7 and select W10 again in Grub, the W10 OS-selection menu appears again.

My questions are:
- Is there any way to start W10 and 7 directly from Grub2 or is the W10 OS-selection menu in the way?
- Can someone explain why a reset is required and a second selection of W10 in Grub2 before W7 starts? Not sure if this is a Linux-related issue or Windows though...