this is just another instance of the 
decimals/locale problem

using 9,7 instead of 9.7 will do it for your 
system/locale settings

future versions will always use . as delimiter
in sourcecode, regardless of locale

didn't see the 2nd paragraph ... :(
... so i'll re-open it for now

but as ceil()/floor() work for me (4.0.0/linux)
could you please verify that it doesn't work
with ',' instead of '.' by changing the source
instead of system settings?

now call me stupid ...
what i was trying to say this time was:

could you pleas try ceil("9,7")
or see what the result of  9.7 - 9 
is compared to 9,7 - 9

You were right - 
ceil("9,2") gives me correct result (10), ceil("9.2") gives me 9. So when I use string parameter and choose correct decimal separator it works just fine. But it seems to me I cannot use float constant assignment.

Let's have this:
$f = $j * $i;
and assign $i and $j to
$i =         2.4       2,4       "2.4"       "2,4"
$j =         5.3       5,3       "5.3"       "5,3"             
ceil($f)     10        ERR        10           13
floor($f)    10        ERR        10           12

It probably is problem with the locale, but I must admit I am a bit confused. Or am I missing something obvious?

now call ME stupid...

This is not a problem of ceil(), floor() but it is really just another instance of the decimals/locale problem as you said before. Excuse me.

so i'll close it now