Do you think that is because of poor flexibility in that area? Or would you say it is because of the heavy amount of strain that is put on that area?
It could be both. With regards to flexibility, can you keep a good back position when you DL from the floor? i.e. is your back straight or slightly arched? If you've got a good back position, then flexibility probably isn't the issue.
The alternative, and common with the desk posture especially is having over active lumbar erectors and / or hip flexors. This is part of the reason why the known functional guys will advise that you don't do bent over rows. Despite it being a great exercise, most ordinary people now a days have overactive lumbar erectors which try and pitch in and take as much of the load as possible - so it makes it less effective whilst putting even more stress on the lower back - the whole 'bang for your buck' thing. It's one of the many issues I had myself, but with constant work on the glutes it just ironed itself out...
It doesn't necessarily mean your glutes are "weak". It can just be case of them not functioning properly or well enough in comparison to the lumbar erectors. For example, a problem i'm having just now is my hams firing before my glutes. At least i'm pretty sure that's the issue, there's a few reasons I think so. All you can do is make an alternation to address the issue and monitor it over a few weeks...
It's actually a strange one - having overactive lumbar erectors, i think anyway. You can actually have overactive AND weak lumbar erectors... Normally people who sit down a lot, and don't train the posterior chain. Just emphasises that everythings relative.
There's a trunk curl up test towards the end of the following article you could try to give you an idea.
Neanderthal No More, Part II
Other than that, if flexibility isn't an issue - do you ever do any 'glute bridges' ? And do you know what 'pull throughs' are? ( i will try and find some pics/videos)
You could try dropping T-bar rows (just for now, replace with something like seated cable rows) and doing some glute bridges before deadlifts (for activation), and adding in pull throughs somewhere (it's an assistance exercise, 12-15 reps per set), which is an amazing exercise especially if you really emphasis the glutes (of course, do it with a straight back as their is a rounded version).
And of course, if you don't stretch the hip flexors, do so. Infact, make it the firs thing you do when you enter the gym before your warm up. If your not sure about it decreasing your performance or not, then I would say just give a try - static stretch them, do your warm up, then dead lift. If your performance is decreased you can come give me a virtual kick in the a$$.
Despite my typical 3000 word essay (half day at work today, so i'm even worse than usual!), it's just a minor tweak that you could try and see if anything changes - hip stretch, Glute activation, and an extra glute emphasised exercise towards the end of a lower body day. And replacing T-bar rows with something else that doesn't cause what you described - temporarily.
With regards to dead lifts, just pay extra attention to form, mainly squeezing the glutes. Even drop the weight slightly to allow you to do it more accurately - or you could switch to rack pulls for a few weeks to emphasise the lockout - finishing with the glutes.
Some food for thought :-)