Same route redistributed into OSPF from multiple routers causes routing loop when route is removed

[naador]

Describe the bug
When the same route is redistributed into OSPF from two separate FRR routers, then the route is removed from the source protocol the route will continue to be advertised in OSPF.

(put "x" in "[ ]" if you already tried following)
[x] Did you check if this is a duplicate issue?
[x] Did you test it on the latest FRRouting/frr master branch?

To Reproduce
Steps to reproduce the behavior:
R1 and R2 with the following configuration
ip route 10.99.99.99/32 blackhole
router ospf
redistribute static
network 192.168.1.0/24 area 0

On each router remove the static route
no ip route 10.99.99.99/32

Run show ip route on each router, there will still be a route installed from OSPF to 10.99.99.99/32 with the next-hop of the other router. If a third OSPF router is added to the network it will show a route to 10.99.99.99/32 through both routers.

Expected behavior
The removed route should no longer be installed in the routing table

Versions

• OS Kernel: 4.9.0-9 (Debian 9.9)
• FRR Version: 7.0.1 (R1)
  (also tested on commit b1c2b44)

Additional context
I first encounter this issue while redistributing from BGP. Also see this issue from VyOS which appears to be related (not my bug report): https://phabricator.vyos.net/T1222

[ton31337]

@naador could you test if this is an issue with the latest releases?