Steps to reproduce:

1. Navigate to the host graph list,
2. Click on 'Create graph' button,
3. Select 'Item' option for 'Y axis MIN and MAX values',
4. Select same item MIN and MAX values.
5. Save your graph,
6. Start Zabbix server to collect Item data.

Result:
User able to save the graph, but on Monitoring -> Host -> Graphs page you will see an error message.

Expected:
On 5th step user should get the error message: Y axis MAX value must be greater than Y axis MIN value.