I'm so happy you managed to figure out the cause! :)
Let me explain a little more on how templating in Ninjaboard currently works, and how it'll work in the future.
In Ninjaboard 1.0 we did two dramatic changes on the template engine that we have in Ninjaboard 0.5.
First of all we started using Nooku Framework. And that allows us to have lots of shortcuts in our template layouts.
For instance, our date shortcut, that transforms dates like this "2010-09-28 14:59" into "31 minutes ago" looks like this:
<?= @ninja('date.beautiful', array('date' => $post->created_on)) ?>
Short and simple.
The next big change, by far the most dramatic, are the auto-skinning engine, codename "Chameleon".
What this does, is enabling you to use any and all of the styling that the site template does for modules, on Ninjaboard itself.
This is Chameleons biggest strength, but also its greatest weakness.
If the module styling in your template doesn't look too great on the forum, then Chameleon wont help you much.
90% of the time, the Joomla! template have module styles that looks fantastic on your forum.
Our Ninjaboard demo site (http://ninjaforge.com/ninjaboard-demo) does a great job showcasing that.
So how does Chameleon work? Since it uses module styling, it lets you configure it the same way you configure modules.
There's a small catch to that though. When you configure a module in Joomla!, you just assign it to a module position, and optionally give it a Moduleclass suffix for style variations that many templates offer.
Ninjaboard is capable of rendering in module positions, but due to unpredictable behavior we have disabled that for now.
Instead of a module position, you have to pick the module chrome that Ninjaboard needs to use.
What's Module Chrome? On each module position, your Joomla! template defines what chrome should be used for how the module renders.
The Joomla! wiki have a great article explaining this:
The easiest way to find out what chrome your template are using for your module positions, are to append &tp=1 to your url.
Each module will then have an outline, and have a small box bottom right saying something like "user1[rounded outline]".
"user1" means the module position, and "rounded" are the chrome.
The way moduleclass suffixes are used in Joomla! templates varies a lot. So I'm gonna give you a few links that shows how they're often used:
So in short, Chameleon needs you to pick a chrome, and optionally a class suffix to configure the style of your forum.
In the future we'll adress the shortcomings of Chameleon by giving Ninjaboard a small set of basic (dark, light, etc) non-Chameleon templates that works better in those situations.
I'm thinking about creating an independent style (defined in current template) for Ninjaboard, if that is possible.
Currently we've not enabled the ability that lets you change what template Ninjaboard is using. We're planning on doing that in the RC release.
But before that, it's possible to override Ninjaboards template layouts, js, css and images by using template overrides.
I don't recommend doing that yet, as Ninjaboards template layouts will change a lot before the stable release, so it'll be a lot of work to keep your overrides up to date.
You could override the css files in Ninjaboard however, and I'll write you a quick tutorial if you want to.
The two bugs you are reporting are indeed real.
The button bug are fixed in the current Beta6, soon to be released.
The avatar bug is still work in progress, but will be fixed soon.
Would you be interested in contributing your dutch translation?
If so, you'll be invited to the beta tester group, and added to the "Credits" section in the "About" popup in Ninjaboard. ;)
In there you'll be able to get the latest nightly builds of Ninjaboard for testing and more.