critical error – inserting text with a link

When i put to any site your great plugin, it has one problem – when i copy a text from other website, that contains link and then when i click the link in the paragraph block, the whole block changes to message “there is an error with this block and preview could not be shown” (or something like this, i have it in czech). And then I have to delete the block and insert it without a link and addthe link again.