if you want to create a clickable url in scribus, you have to put a link shape on top of the part you want to be clickable.
a bit odd, but true.
from your description you don't seem to have done it, so i have to guess that the text in your pdf is not clickable.
but: often, pdf readers try to track the urls in the text make them clickable.
this is probably what is happening in your case.
having http becoming h6pt seems a bit odd to me. but you have to be aware that PDF are created for print and there is not guarantee that the text is stored in a linear way. you probably have already experienced that you cannot always properly select the text in a pdf. even more so when you have multiple columns. the pdf reader has to guess what the original text flow was and might get it wrong.
personally, i'm keen to think that this is what is happening, but i have a hard time explaining a "h6pt".
if you share a pdf showing the issue it might get easier to provide you with further help...