There is nothing wrong with ceil, and there is no "weird behavior".
You need to learn that computers do not have infinite precision, and that computing with floating-point numbers is not the same thing as performing mathematical symbolic operations.
Floating point numbers are how decimal values are stored in your computer: they do not have infinite precision, and they can only approximate many values. Even if it looks like the "actual" value is being shown to you this does not mean that the internal representation inside your computer is the same value.
Of course this means that every operation you perform on floating point values will accumulate these errors. It is up to you (and every other programmer) to design programs that take this "floating point error" into account.
Read all about it:
And if you want to see what the decimal equivalent of a floating point value is, then try this FEX submission:
As its author points out: "Don't confuse the exact conversion with significance!"
