Tribunal makes a correction which is not a correction…

I’ve received a ‘corrected’ decision on a DLA appeal, which moves the date of award forward by a month. 

This would appear to be in response to representations from the DLA unit, who believed that the health problems leading to the award were a sub arachnoid haemorrhage with a specific date of onset.  They did not make such representations in their submission.

In fact, the award was based on the appellant’s longstanding arthritis problems. 

So - the correction is clearly wrong. 

Is it a new decision, meaning we’re in time to request reasons?  (otherwise we’re beyond the month) 
Do we simply apply to correct the correction?

I would ask them to correct the correction. Has the “correction” been made by a different judge?  I had a similar case some time back and it was resolved fairly easily, so hopefully same will apply here.