Created attachment 925897 [details]
it displays none but there are 6 plans in the tab after submitting these two plans

Description of problem:
as summary

Version-Release number of selected component (if applicable):
v3.8.10-1 on devel server

How reproducible:
100%

Steps to Reproduce:
1.open a test case,https://tcms-devel.app.eng.nay.redhat.com/case/293344/
2.then select the Test Plans tab,check how many test plans there are.
3.then input two plan ids:10147 and 10148,click add button.
Then check whether these two plans can be added in the list.

Actual results:
step 2: there are 6 plans under this case.
step 3: 
(1)after adding these two plans,it display "No plan found for this case."But it shows 6 plans in the tab.
(2)then refresh the page,all the plans are listed in the tab,but the 10147 and 10148 are not added into the plan list.

Expected results:
step 3: 
(1)after submitting these two plans,it should display 8 plans instead of 6.
(2)and it shouldn't display none and shouldn't need to refresh the page 

Additional info: