Am 15.05.2011 um 12:39 schrieb Taco Hoekwater:

> On 05/15/2011 11:35 AM, Steffen Wolfrum wrote:
>> Hi Hans,
>> 
>> while finishing a big project (900 pages, 300 floating tables/figures) I noticed that the first line of each page is moving up/down (almost half a line)!
>> 
>> Reason: As soon a a floating object is placed the next page is disturbed.
> 
> The problem is that the vertical space collapser is collapsing *into*
> topskip's spec field, thereby changing its value. That much is
> clear to me. I do not know how to fix this nicely, but a crude
> workaround to fix your project is:
> 
> \appendtoks \global\topskip=10pt plus 50pt \to \everyafteroutput

What about \setupinterlinespace[top=0]? 

I had once a related (?) problem:
http://archive.contextgarden.net/message/20110224.131537.352b2342.en.html 

Greeting
	Andreas