Sloooowwwww text entry in InDesign CS5

Question

I've got a truly bizarre behavior that is driving me crazy!  About midway through a document, text editing becomes painfully slow.  I can type a sentence and it takes several seconds for the cursor to catch up.  This happens whether I edit in place, or type in Story Editor.
Here is where it gets very bizarre.  In any text BEFORE this point in the document, text entry and editing is fast, clean, and efficient.  The point in the document where the change from fast to slow takes place stays the same, REGARDLESS OF WHETHER I DELETE SOME TEXT.  In other words, I've found the precise paragraph where the slow typing starts.  If I delete that paragraph, then the NEXT paragraph shifts up and becomes the start of slow editing.  Paragraphs before and after this point are all styled with the same body paragraph style, so it has nothing to do with the style itself.  In fact ANY style below the "magical point" in the document has very slow typing.  Any style or paragraph above this point types and edits fine.  It almost seems like this magical point happens after a certain number of characters in the document.  If I delete text above this point, the magical point shifts further down the document text.
Thinking I had a corrupted file, I exported the entire file as IDML (InDesign Markup) and reimported it.  I get THE SAME BEHAVIOR IN EXACTLY THE SAME SPOT.  The file is about 11 pages long and consists of one story that runs through threaded text frames.  There are about 5 images that have been anchored to text.  (But not near the "magical point" where text editing becomes as slow as molasses.)
I've tried making new documents, changing styles, loading different master pages, deleting the images, deleting the master page, etc. and nothing affects this issue.  And yet I can create a new document, fill it with a hundred pages of placeholder text and I don't get this behavior anywhere in the document.
Has anyone else experienced something similar??  It's MADDENING!!

Answer 1

This is definitely an issue in the Windows environment that has absolutely no impact in a Mac environment. I was just introduced to it, and I'm really scratching my head.  I do most of my layout on a really nice Intel Mac using ID CS5, and I'm currently working on a huge project with multiple team members working on a variety of computers. I was unaware until yesterday that one of the team members who is working on a Windows 7 laptop was having problems making text edits in documents that work just fine on my Mac. There was a severe lag when typing. She could go get a coffee while waiting for one simple typed sentence to appear on the screen. We opened up system resources and everything is maxing out while text is being typed, CPU, memory, network. It's a real stumper. This is not a simple machine, it was purchased to be a graphic design computer and has really good specs, but just to make sure it wasn't the computer, I tried it on two other PCs. One is my laptop that I freelance on and the other is a fellow designer's machine that has absolutely amazing specs (actually better than my Mac), both running Windows 7.  On all three computers I have the same typing lag, though I can reduce the lag some by turning off everything that saps ID performance (auto preflight, screen redraw, dynamic spelling, balance columns, etc.).  The files are on a server, so I even tried copying them to the local harddrive and severing link and InCopy connections. I've tried turning off balance columns and still the lag.  The lag is most prominent in a fairly complex table and I've noticed it is worse when editing text that is on a 10 percent black background. 
I can provide a file to play with if anyone wants to see the behavior. I can reproduce it on any computer with a Windows environment (both CS5 and CS5.5).  I would appreciate a fix either in the way my documents are created or for the app because I'm doing hundreds of these documents for the next couple years and this lag is a severe problem in our workflow.