I can reproduce this in a slightly different way:
- Right-click on a top-level tab that has children and click Close Tree
Expected: restored tabs work as before.
Effective: the tree will be reinstated correctly and all tab labels will match, but either some or all (it’s not consistent) of the restored tabs would be blank. The address bar would be empty and the tab would show the start page.
There’s data loss potential: having lost tab URLs it may be tricky to locate what was open before (searching history by tab labels seems to be the only option left and it’s not very reliable).