Cannot upgrade from 4.3 to 5.1. Version is not correctly detected

Question

Here is the output of the process:

./atlassian-jira-5.1.1-x32.bin 
Unpacking JRE ...
Starting Installer ...

This will install JIRA 5.1.1 on your computer.
OK [o, Enter], Cancel [c]
o
Choose the appropriate installation or upgrade option.
Please choose one of the following:
Express Install (use default settings) [1], Custom Install (recommended for advanced users) [2], Upgrade an existing JIRA installation [3, Enter]
3
Existing installation directory:
[/mnt/sdb1/jira-4.3.1]

Sorry, we are unable to automatically upgrade your JIRA installation as it is not version 4.3 (or later)
For more information see our documentation at the following URL:
http://docs.atlassian.com/jira/docs-${jira.docs.version}/Upgrading+JIRA+Manually
Finishing installation ...

Well, it turns out i'm running 4.3.1. What's wrong with it?

fernandomm · Answer

I generated an export and found this at the begging of the file:

___ Environment ____________________________

JIRA Build                                    : 4.3.1#615-r147022
     Build Date                                    : Fri Mar 25 00:00:00 CET 2011

Is this what you asked?

Nic Brough -Adaptavist- · Answer

Ohh, now that's a really interesting one then!  Could you also check the xml files in the Jira home directory (I don't expect them to tell you anything odd), and unzip and open the export file and check the first few lines - that should contain the version it thinks it was exported from (and is the interesting one, as I think that's where the problem is.  Not that I know how the wrong version gets in there!)

fernandomm · Answer

I double checked. It shows 4.3.1 and build number is 615.