Are you using the TinyMCE Editor when you edit modules and articles?
We use
RokPad
to put in content so we can place more code in there that would normally get stripped out by the editor. If you opened these modules with the TinyMCE editor on and then saved it, it may have stripped out or changed the code slightly.
If you need to find a uniform height that the modules will stick to, even if there is more content in one than the others, pick the tallest one and find a height that works for it, then add this to all 3:
<div style="height:300px;">
YOUR MODULE CODE HERE
</div>
You need to enter this in without the TinyMCE editor on and you can change the 300px to whatever you need to make it work.