Increment Count Doesn't Work

[r2d2]

On Jira, I have a field called re-opened count which in essence every time the bug is re-opened the count increments however I've noticed this only works if it doesn't have a count present once we hit the count of of 1 this no longer works. Any ideas why this is?

The code is as follows: - 

{{#=}}{{customfield_10401}} + 1{{/}}