I can't quite get the aspect of **that** in the following sentence:

> 
> This is causing a problem now **that** the moveElement function is being called whenever the user hovers over a link.
> 
> 
> 

My friend who is a native English speaker explained that you could easily substitute **that** for **because**. I can do that and the sentence will make much more sense but still the word being used is not **because** - the author opted for **that**. What nuance in meaning does it have?