some PDF's to iPhones via ActiveSync are corrupt

we have two server applications (one .NET/ASP web app, the other a native Windows app) that generate PDF's that are then emailed to our users on Exchange 2010. the apps deliver the emails to the Exchange server via SMTP, and our iPhone/iPad users receive their email via activesync.

pretty much all of the PDF's generated by the web app and many of the PDF's generated by the Windows app fail to open on an iPhone or iPad. tapping the attachment shows the screen that would display the PDF with the name of the file at the top but the bottom of the screen is completely grey.

one thing i have figured out is that the attachment on the iPad is uuencoded. forwarding the attachment to another email address shows the uuencoded format. here's a sample:

begin 600 unknown
M)5!$1BTQ+C0-)>+CS],-"C8@,"!O8FH\/"](6S8U-B`Q-#A=+TQI;F5A<FEZ
M960@,2]%(#DQ-#8O3"`Q,S`Q.2].(#$O3R`Y+U0@,3(X-3,^/@UE;F1O8FH-

---snip---

M,C8T,"`P,#`P,"!N#0IT<F%I;&5R#0H\/"]3:7IE(#8^/@T*<W1A<G1X<F5F
.#0HQ,38-"B4E14]&#0H`
`
end

whereas the normal version of the file looks like a normal PDF:

%PDF-1.4
%âãÏÓ
6 0 obj<</H[656 147]/Linearized 1/E 9698/L 13571/N 1/O 9/T 13405>>

---snip---

trailer
<</Size 6>>
startxref
116
%%EOF

so i think the problem is that the attachment is being double uuencoded somewhere, or the iPhone is failing to recognize that the attachment is uuencoded and not decoding it.

any suggestions on where to begin troubleshooting this problem?