I downloaded the 1.5.10 upgrade files to patch my 1.5.9 board, however after uploading and overwriting existing files I noticed that it did not take the forum offline for upgrades, and going to /forum/install still shows 1.5.9. I have tried rebuilding the master templates but there was no change. To confirm, all files uploaded and overwrote successfully and were uploaded to the correct location.
If it is still showing as 1.5.9, either the files haven't been uploaded to the correct location or some sort of server caching is preventing the new files from being served (or you uploaded the 1.5.9 files).
If you are sure the files have been uploaded correctly, flush or disable the cache (your host can help with that if you aren't sure how to).
Good call on the caching. It could very well be that as we do use Incapsula CDN. By upgrade files I meant the upgrade package from the customer area. I will disable caching and get back with further updates. Thanks a lot.