Fillable PDF becomes unreadable after edited with Okular

Can anyone explain why a editable pdf becomes unreadable after edited with okular?

Unreadable by what?

"editable PDF" is a bit of a misnomer. PDF isn't a WYSIWYG word-document or desktop publishing format, it's a printing format, already boiled down to the point where handy things like word-wrap and such cease to exist. As such, editing them is always a bit dicey.

Everything but okular.

Sorry I used the wrong terminology. It is a fillable pdf. Something like this. Can you please fix my title?

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CDoQFjAA&url=http%3A%2F%2Fwww.thewebjockeys.com%2FTheWebJockeys%2FFillable\_PDF\_Sample\_from\_TheWebJockeys_vC5.pdf&ei=RxJGUvvHF4KG9QT7hYGoCw&usg=AFQjCNGJlnGGXWli-Fmx1OsCAhintZKlqg&sig2=Gsujvvl3jYyZgHggYfvL2Q

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&ved=0CEwQFjAC&url=http%3A%2F%2Fwww.worldofprinting.com%2Fsample\_pdf.pdf&ei=RxJGUvvHF4KG9QT7hYGoCw&usg=AFQjCNHStuaY2h9r0COWlKli2v6l295Q7g&sig2=WAFao9M2_C8qNmN4Jatctg

Bug in Okular? According to Okular - Document format handlers status PDF form support is a work in progress.

Can you recommend a Linux PDF program that properly handle fillable pdf's?

There is such a thing as Adobe Reader for linux.