MTOM Decoding Failure for Attachments Help

Let me first say I'm an extreme novice for forums, SOAP testing, and understanding MTOM, so I appreciate your understanding and patience with me.

I have two questions in regards to MTOM encoding with attachments (XML text files).

1) If the attachment file contains a space in the file name instead of an underscore (Base Attachment.xml vs. Base_Attachment.xml), an MTOM encoding fault is tripped when the request is sent.
Why is that the case? Is that a valid MTOM encoding error? Should the attachment work or should it fail and why?

2) One of my tests does not require GZIP Compression and should be a successful request. However it's also tripping an MTOM encoding error. The really odd part of this question is that in June, 2013 with SoapUI 4.5.1, no error was trip and the request was successful. When I upgraded to the SoapUI 4.5.2 in July 2013, the error first appeared. However, at that time it was still passing successfully in 4.5.1 and only failing in 4.5.2. Now that same request with GZIP compression set to none generates the MTOM encoding error in both 4.5.1 and 4.5.2.
Is there a setting that needs to be adjusted in SoapUI? Any ideas what the error is occurring?

Thank you.